Does it have PCI-E or AGP? And, the only problem that might apply is that the card might not be able to fit in the case. As well as the case might not be able to cool it properly. A 480 watt psu is enough. And why not consider the 4850 or the 9600GT? the 9600GT is slightly slower, but cheaper. The 4850 is much faster and only a little more expensive.. my opinion: go with the 4850.
Thanks for that quick respond on my message . With new graphic card I just woried about that then my motherboard could be to weak , I dont have to big experience in this things, thats why i consider geforce 8800 and price range between 8800 and 9600 because suits me better, but I am really suprise then I could put in so good graphic card. On my motherboard I have PCI-E. Once again thanks for this message i hope some other people with the same computer will find answers with this topic here . P.s sorry for my english .
The problem I can only see is the power supply. You know, more powerful hardware requires more powerful power supplies. Sure you can use that 480W power supply, especially if it's a good one. But I suggest at least a 500W power supply anyway.