Upgrade my computer for ~£100

[Chronicle]

Hi
I am thinking new PSU or new GFX card (gonna get them 2nd hand to save money - in the MM)

Current specs -
Asus 9600XT
KV8 Pro
Generic 400W PSU
3200 Newcastle (754)
2x 512mb ram


Plus things like CD/DVD etc but they arn't important

What would you upgrade, if you had approx 100 quid to spend. I only really WANT to spend about £50, but will go upto 100 if its worth it.

 

[Chronicle]

Forgot to say, i'm having some problems with my computer, nad have had for sometime, it always crashes when i play games, so I want to upgrade more than one thing (esp if spending £100), so ill be able to at least tell if it wasn't a certain part causing crashes.

I was thinking a cheap x800, and a new psu. But i dunno.