Value 4 Money

Hmm, a Pentium D will seriously bottleneck any graphics card over $120. And your PSU is probably generic and cant handle any more than a 250W load.

I'd suggest getting a HD5770 + decent 400W PSU, and save up for a much needed processor upgrade.

Asus HD5770 - $115
http://www.amazon.com/gp/product/B0033KBT68/ref=as_li_q...

Antec EA430D - $45
http://www.amazon.com/gp/product/B002VLYJRG/ref=as_li_q...

Corsair CX430 - $45
http://www.amazon.com/gp/product/B004W2T2TM/ref=as_li_q...

Before I can give you a informed answer, I'll need to know your graphic quality expectations and if your Motherboard has a PCI-E, AGP or PCI slot. This is because your system is very out of date but it's still worth investing into a GPU for you to get the most out of your current system. As long as your realistic with what you have, you can easily play those games you mentioned at 1280 by 1024 resolution w/ medium/low quality settings. But with what I know so far, I'll recommend a AMD 5670 or 6770. It will run you only about $75-85 but with your current CPU, that's might be pushing it. And as a side-note, stay AWAY from "Powercolor" GPUs.... you've been warned!! @_@;;

@Zero_ I'll have to disagree with your suggestion b/c a 5770 will get seriously bottle-necked by his CPU - on top of the fact that it costs more and he will "probably" need to get a new PSU to go with it. Also, I wouldn't recommend getting a new CPU either b/c your currently running DDR2 Ram as well, any investment beyond the much needed Graphic Card will have diminishing returns in terms of performance - your better off getting the GPU I mentioned and start saving up for a new PC.

~Coffee

My MoBo burnt out. I was planning to switch to an AMD MoBo and buy a Phenom II X4. Will that be good? (i have a 450W PSU)

Yeah, that's a very economical decision (performance vs price ratio). I'd suggest getting a ATI 6770 graphics card to go with your new PC, your PSU can easily handle the load and more.

~Coffee