Here is the information I found on my power supply.

ATX Switching power supply

AC Input 230 VAC 50/60 HZ

DC Output +3.3V +5V 5V +12V -12V
25A 32A .3A 17A .8A
+5 VSB COMPS-ON PWOK
2A ReturnRemote PG

My system specs are:

Pentium Dual Core CPU 2.8GHz
1.5 GB RAM
160 GB Harddrive

No. I looked through a bunch of 8800GT product pages, and finally found one that mentioned power requirements of 28A on the combined 12v rails. You have 17A on yours. Your PSU will choke if asked to power this card.

What about 8600GT? Can my power supply handle it?

Yes, but.... If you were considering an 8800GT, the performance of an 8600GT may be very disappointing; AND, what brand and model is that PSU? If it is a cheap one that came with your case, it may not be good for its rating, and may have difficulty even with the 8600GT (which needs no auxilliary power, btw). What GPU do you have now?

I have a 7200GS. Is 8600GT going to be a big improvement?

If you can afford a new power supply this one will power an 8800gt with no problem - (great reviews/plenty of power)

http://www.newegg.com/Product/Prod [...] 6817182016

I'm not sure how much improvement an 8600 will make, but an 8800gt will be like night and day!

Rosewill PSUs are tier 5 junk.

Official XS Tiered PSU Manufacturer Brand Listing Phase IV Beta

So which card do you guys think is the best for my power supply? I don't want to change my power supply. I have read some good reviews for 7950GT. Can my power supply handle it? Is it better than 8600GT?

I use a Enermax 500 Watt PSU to power my 8800 GT. Runs great. Most of their PSU's are modular too - avoids clutter. They always have good amperes on the 12 volt rails to support today's GPU's. I don't think they sell my model anymore. I'd suggest choosing one of their 600 W ones.

Kind of. Some games that refuse to install on the 7200GS will install and run badly on the 8600GT, as in a few fps. Think Powerpoint slides...

Jacques, is your 7200GS AGP or PCI-E?

How much money do you have, for PSU+video card together? For example a 7950GT costs $250 at newegg, and for that money you can buy a StealthXStream 600W and an 8800GT and get several times more performance.

Edit: one more thing, are you in Canada, by any chance?

Your current PSU is not going to safely handle anything over an 8600GT (or 2600XT if you prefer ATI).
And yes, an 8600GT will demolish a 7200GS. There is a nine-tier difference between them in the chart Cleeve includes at the end of his best card for the money roundup.

I have a PCI-E slot and I am in India so it is not possible to buy the PSU models you guys are recommending. If I want to have 8800 or 7950 what kind of PSU do I need? Watts and amps?

For 8800GT:

http://www.newegg.com/Product/Prod [...] 6814143118

In general, you can use newegg's site to get a lot of info, like I just did here.

7950 GT:
http://www.newegg.com/Product/Prod [...] 6814143071

So for 8800GT I need 425W PCI Express-compliant system power supply with a combined 12V current rating of 28A or more. I think I got everything I wanted from this thread. Thanks for the help guys.

Get a good PSU.