GeForce® 9800GT 512MB HELP"!"

No you need a 400W PSU. Get a good quality one, from corsair, PC power and cooling, OCZ, Antec, thermaltake, tagan.......

I would avoid the green or E editions since they are known to have problems with some boards. Get one that has a 6pin power connector and 400w is more than enough to run even a older 65nm 9800gt.

Yes, I agree, avoid the Green Model Video Cards!! They are very buggy and will crash your computer more than normal. I've tried a lot of them.

It may run with a 300W PSU, but that is of course assuming that PSU can sustain 200+ W while gaming for more than an hour without crying for it's mommy. Unless it's a high quality unit, I doubt it will survive very long without blowing out, that's if it doesn't blow the first time you try and play a game anyway.

For you weak PSU, the best you can do is a GT220 and maybe a GT240. The 4670 and the 5670 use more power than the GT240 so I wouldn't consider them with that weak PSU.

If it looks as it does in the pic you should be able to replace the PSU unlike some Dell computers (Dell hell).

There is only like 10 watt difference on load between a gt240 and 5670 or 9800gt green. Max power draw from pci-e is 75 watt anyway, seems like it won't make much difference.

I have a 300 watt as well, lite-on power supply in acer prebuilt. It says up to 20A on 12V rails, hopefully it will power a 5670 okay. I think it will be okay since my core 2 quad Q8300 doesn't draw too much power.