the card mentioned is good enough to run Oblivion on medium settings. you should Try Geforce 9500 GT PCI 1GB DDR2, which is faster by a significant margin, only being about $10-15 (Canadian) more. but I suggest you to go with your current choice, you can't squeeze a LOT of power out of PCI.
The Geforce 6200 (original, pre-"A" castration) was the last card that didn't outrun the plain PCI bus's extreme limitations. It was inadequate to run this game at an acceptable frame rate, without the post-patch "Ultra Low" graphics option.
All newer cards that still have a PCI bus interface will be no faster than the old 6200 was. There is no acceleration possible, and 33 MHz is just plain too slow for ordinary graphics purposes, let alone for games. You could have an adapter of some sort to allow an HD 5970 (world's fastest) to plug into plain PCI, and it would be choked down to Geforce 6200 frame rates.
All of the Compaq / Dell / HP / Sony junker PCs sold without any video bus have cheap power supplies, were sold with slow RAM (single data rate, likely), cheap drives, etc. everything about them was low quality.
It's a total wast of time to upgrade such crap these days. Local thrift stores here in the states have better PCs for sale for less than a plain PCI card costs, with keyboard, speakers, and mouse included, that are better able to run this game than anything like this system is could ever do.