Can you give us a screen shot of the GPU-z report, there is a little camera icon on the report for this.
It could be that it is being miss identified by the program. they used a G73 core for the 7300 GT and teh 7600GS. its feasable that they used some low performing 7300GT cores for the GS version an dits confusing the program.
If you can show us the report then we can match up some of the performance data and hopefully work out what card you have.
Run the program then click on the little camera icon, select free image hosting and click copy on the first link. Come back to the forum then click and paste the link in like so. http://gpuz.techpowerup.com/08/06/09/7p8.png
how is it possible ....and it is only 128mb.
But when i have purchased and even on the box they have written
nVidia GeForce 7600GS 512mb. what to do now plzzzzz help me.
This is possible, especially if you bought an "open box" product, though it can happen on a box that was labeled as new. Unfortunately, from time to time, someone buys a new card (or other piece of hardware), sticks their old card in the box, and then return it for a refund. The mail order company doesn't happen to check it out, except for making sure the manuals and wires are still there, and then they resell it. Then somebody else buys the new/old card. If their old card was slower, they see an increase in performance and are somewhat satisfied. Or they may see a decrease and blame it on the company that made the card, be it ATI or Nvidia. This is one reason that the instruction manuals start out with telling people to inspect the card and the various other pieces that are supposed to be in the box before trying to install anything.
Wondering if you bought the card in a store or eBay or something? I can attest to what Sailer said above. Years ago I worked at a major electronic retailer. We saw that kind of stuff all the time. Even had a guy buy speakers for his car, and "return" them. When the box was opened there were bricks in it instead of speakers.