I am a gamer spending about 4~5 hours playing stuff like OBLIVION which is veryyyyyy resource demanding.

so how can i optimize my pc for gaming.

i am only interested in gaming along with a little bit of internet surfing.

My rig is a modest one with :-

pentium 4 516 2.93 GhZ.
1 gb ddr ram
128 mb nvidia 6600gt.
other things qare normal.

What do you mean know your power supply?

If you mean the wattage, you can open up the case of your computer. That shouldn't void your warranty, and the details should be visible on a sticker on the PSU itself.

As long as you don't break those stickers which say "warranty void if broken", you'll be fine.

As for your rig...

A graphics card upgrade is a must if you're into gaming. The oblivion is a very huge resource hog, and therefore, the more money you can put into your graphics card, the better it will run.

It might be a good idea to upgrade your CPU, RAM and Graphics card if Oblivion is the main game you play, as it is very taxing on all these components. An extra 1gb of RAM should show some improvement for a pretty low cost, and the newer Core2Duo would show a little more improvement than the RAM would in certain areas.

But the bottom line is that your graphics card is the main bottleneck for your gaming, and would be a very good idea for you to get the biggest you can afford for that game, even the 8800gtx may struggle with it (depending on resolution of course! 800x600 will run pretty well on cheaper graphics cards...)

i dont think you understood the question tha quesyion is that how do i modify the registry or use some sort of software or any changes in windows to make it ideal for gaming i know thatit will not be a very major change but if you get a little performance for nothing then it is very good.

hope my question is clear now

Have a look on Tweakguides. There's quite a few game guides as well as the TGTC, a Windows tweakguide.

I would follow peterdiva suggestion, going to that website =]
i go there alot often to tweak and kill movie intro etc, very good site.

what we need is simple answer for simple question like that ;p

but if you really into Oblivion and have a minimum video card to support, i suggest going here and DL Oldblivion, i haven't use it yet since i don't need to, but i heard friend said its good =]

http://www.oldblivion.com/?page=screenshots