Well the first thing you need to do is backup your data, either by putting your hard drive in another computer as a slave or by using a Linux live CD and a USB stick\removable HDD.
From Linux you will be able to look in your computers hard drive and see if there are any DMP files which are usually left with BSOD.
In Windows 7 you can find it at: 'C:\Windows\Minidump' XP should be the same.
If you have access to another Windows computer then copy these files to a USB stick and use a program like WhoCrashed and\or BlueScreenView to read these files to see what is causing your problems.
You could also follow this guide but you might find it confusing depending on your level of experience with computers.
http://forums.majorgeeks.com/showthread.php?t=35246
