The 6150SE is indeed a terrible graphics chip. Your best bet for reasonable money of a card that will work in almost any system is the Radeon HD4670. The only occasions when you won't be able to use those is if you have a thin compact tower. Get back to us with what PC model you have and we'd be able to say if the 4670 would work or not.
i have a compaq presario, its a late model 2008, and only the Graphix card, is bad. i been lookin at the NVIDIA 9800 GTX, everyone i talked to said that would be best, its SLI compatible, and its runs at like 57.8 GB/s, ehich is all i need.
The 9800GTX is a last generation card, even the 9800GTX+ is older generation, I don't know who you've been talking to, but they're all a year behind on what hardware is worth buying, if not more.
The memory bandwidth figure of a graphics card is also completely irrelevant for how well it actually performs.
The 9800GTX+ has been replaced by the GTS250 here:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814162029 That's nvidia's current midrange card. It is much more efficient than the 9800GTX+ and slightly faster as well.
However, this is all redundant if the Power Supply in that system is proprietary. A lot of PCs, usually HP/Compaqs and Dells use Power supplies that are a different shape to normal and usually can't be replaced with anything but identical units. The power supplies these systems come with are not designed to run powerful graphics cards, which is why it's always a stupid idea to buy a PC with a basic graphics chip with the intention of upgrading it later, it's always huge hassle.
Right now, you can either buy a nice lightweight card that won't stress the power supply or cooling in that PC too much, but won't give you as good performance (it'll still be way better than the 6150SE, by a factor of at least 10, if not 15) and these cards are nice and cheap.
OR, you can replace the case, power supply and depending on how Compaq built the system maybe even the motherboard as well, so you can fit a proper graphics card in there without any restrictions on how powerful it is. it's your call, simplicity and good performance, or complexity, substantial cost and excellent performance.
This is the simple option: http://www.newegg.com/Product/Product.aspx?Item=N82E16814102820
