|"I have a "BUYMPC D865GLC" with Pentium 4 CPU computer which I bought almost few months back"|
Socket 478, DDR memory, AGP - you bought a 6-7 yr old system! I sure hope you didn't pay much.
AGP is a dead end, it was replaced by PCI-express several years ago. Any decent AGP video cards that are available these days are generally very expensive when compared to their PCI-e counterparts. In fact, there are no really good AGP cards available anymore. NVIDIA pretty much abandoned the AGP format but ATI hung in up to the Radeon HD 4000 series. Even so, there have been a lot of driver issues with the "modern" ATI AGP cards.
Probably the best AGP card you can get is the Radeon HD 4670 but it's well over $100. The PCI-e version of the same card sells for 1/2 the price.