if its a 230 watts smps then change it immediately .. even if its not i always suggest going for a good branded smps such as antec,coolermaster , powersafe etc. go for powersafe 400w gold plated smps which will cost around 1500/- bucks. i dont guarantee that it will stop the blue screens though... for the blue screens try the following,
Run Memtest86 on your ram for atleast 2-3 hours. get it from
www.memtest86.com
Check for loose / faulty cables.
Update all your drivers for all devices (modem,vga,sound,etc). perform a clean reinstall with xp sp2.
Flash your BIOS to the latest version.
Make sure your RAM is running at the specified timings and not below them.