i do not offer any guarantee of the process below working for you....the wind might be blowing in the wrong direction, or the planets might be slightly out of alignment, or perhaps a butterfly somewhere on the other side of the world flapped its wings at the wrong moment, causing you to end up with a very expensive doorstop.
if you've never installed an operating system before at the very least go and find someone who has and talk to them before attempting it.
before starting, a document that's worth a read is
[Edit 20161115: the PDF at the above URL has been superseded by the support article at the below URL]
this describes in some detail the order in which drivers should be installed following the installation of the operating system...quite an important factor given the nature of the hardware inside the machine.
if you have purchased your Precision M6600 new then hopefully you ticked the relevant boxes during the purchase process to make sure you received your Win7 recovery disk, and the driver/utility discs for your system.
if not, then you'll need to obtain a copy of Win7, and manually download the hardware drivers from the dell website
if you're not running the latest BIOS (version A07 at time of writing) then this is a good time to flash it. (warning: this could brick your machine so proceed at your own risk)
now you can download the drivers you'll need.
[Edit 20161115: see Dell support article for driver list,
at this point you may or may not choose to remove the two dell recovery partitions from the machine in order to get some space back on your primary drive. if you do choose to remove them i strongly suggest you make a backup of at least the partition containing the recovery image (the larger of the two) in case you need it later. for example, you might want to sell the machine at a later date with the factory image loaded back on. (Hint: if you want to restore from the backup of the factory image, google search for things like "dell recovery imagex" and "waik imagex". maybe i'll get bored and do it one day for a laugh and write a post on it)
i chose to backup the factory image to an external hdd using a linux liveCD (ubuntu is a fairly safe bet, but to each their own).
use dd and gzip to compress the partition(s) onto the external hdd.
dd if=/dev/sdc1 | gzip > Partition1.gz
to restore this at a later time (assuming you've recreated the partition table exactly as before)
gzip -dc Partition1.gz | dd of=/dev/sdc1
use something like fdisk to list the partition table and then note all the details somewhere safe, or save a screenshot or something.
N.B. if the external hdd you're using is formatted in a file system that is limited to 2GB files (eg. FAT32) then consider using dflcdd to split the output into suitable chunks.
now use gparted to remove all the partitions from the primary drive.
my Precision M6600 has a mini-SSD for the primary drive, with two 750GB secondary drives in a RAID0 stripe for storage.
an annoying feature of Win7 setup is that it wants to create a reserved system partition during the install and in my case it tries its best to put this system partition on the RAID stripe, for reasons known only to microsoft.
if you can 100% guarantee that your disk configuration is never going to change...ever...then that's not a problem. but i will likely upgrade the disks as larger sizes become available so having the reserved partition anywhere but the primary drive is a no-go.
in order to get around this issue i had to physically remove the secondary disks from the machine. fucking ballache, thanks a lot microsoft.
so...booting from the Win7 disk...select your language etc.
before you get carried away and click install, press shift+f10 to get to a command prompt. use diskpart to make sure there's no traces of old partitions left lurking...
sel dis 0
cre par pri align=4096
for quick fs=ntfs
this will select disk 0 (there's only one disk in the machine so it must be 0...if you're attempting this with multiple disks present use lis dis to see the list first), clean it, create a primary partition, format it NTFS, set it as the active partition, then exit.
close the command prompt, click the install button. choose custom installation when prompted. it will ask where to install it, choose the disk (in my case, the only one in the list) and then hit next. it will now install to that disk....go and make a cup of tea, it takes a few minutes.
with a bit of luck you'll eventually be presented with screens asking you to choose a username, password, set the time etc and then you'll end up on the desktop.
a quick look in disk management confirms that everything is in one partition on the SSD
next turn off the swap file and reboot. no need for it really with 32GB of RAM. if you have less than 8GB you probably want to keep the swap file in place. you could always move it to a different disk for a slight performance increase.
now to put the other disks back in...
shutdown, reinstall the disks.
switch on, hit ctrl+i at the relevant point, create the RAID0 stripe. reboot, hit f12 to get the boot menu and make it try and boot from an empty CD drive. (for some reason the boot list doesn't always update properly, but forcing an unsuccessful boot attempt seems to make it update).
reboot, go into the BIOS and check the boot order is set to the mini SSD (the raid controller by default prioritises the stripe for booting over the mini SSD for whatever reason).
reboot and let windows start up, hooray!
now you can start installing the drivers you downloaded earlier.
N.B there'll be plenty of restarts during this, so configure windows to automatically log you in...
start > run
untick "users must enter a username and password to use this computer" and click apply
enter your password and click ok
now when you restart you'll automatically be logged in
to change back afterwards, just run netplwiz again and tick the box.
the driver install order
[Edit 20161115: see Dell support article for driver install order,
when complete, do a restart, then run devmgmt.msc to check that there are no exclamation marks next to any hardware items.
you're done, carry on loading software etc...
N.B. now would be an opportune time to take an image with Norton Ghost, or a free alternative such as g4l. that way you can then easily restore to a clean state in the future.