I was wandering aimlessly through some technology blogs and found the blog of a writer for PC Pitstop who also wrote a comprehensive tool for diagnosing Windows performance issues. In particular he wrote a post about a way to improve performance by emptying the Temporary Internet Files folder  which is a very valid point - Internet Explorer permeates every facet of Windows these days, and has ever since Windows 95 OSR2.
I posted a comment stating that there was another way to do this - and it is something I do on every machine I build - to give the swap file, system files and your data separate partitions.
A general rule of thumb for swap partitions (which had a home in Unix based operating systems) is between 2 and 2.5 times the amount of RAM in your system. The system partition is a tricky one - you have to account for not only the system itself, but for any applications you're likely to install. A good rule of thumb is 16gb for Windows XP and 40gb for Vista/7.
So let's put this into perspective: say you have a 500 gigabyte drive and we wanted to install Windows 7 on it. Our system has 4 gigabytes of RAM. Here's what we'd do:
C: (System) - 40GB (create this, install, then create the other two)
D: (Files) - ~ 415GB*
E: (Swap) - 10.5GB
* = this value will vary depending on the true size of the drive - I used 500 billion bytes as an example.
Once you've set this up, right click on Computer in the Windows menu, click Properties, click "Change Advanced Settings", click Performance, select drive C, disable swap, select drive E, set the size minimum to by 89% of the drive - otherwise it'll be whining at you that drive E is getting full.
This has twofold benefits - one, by moving the swap file away from the system drive, it prevents it from getting fragmented as new applications get installed, so a fragmented system drive won't cause as many performance issues as they otherwise would. Two, if you need to reinstall Windows for whatever reason, there's no need to backup your data as it will still be in the same place after installation. That said, you should backup anyway in case of any other "mishaps" that may occur from time to time.
 Bits from Bill: Free #1 Tweak to Improve Windows Performance