My Desktop PC, although 8 years old has most of what I need. However, is it possible to replace the AMD Duron 900mhz processor with a new quad or intel i5 processor. If possible what would be the approximate cost.

Hi, the short answer is no, for a few reasons.
Your motherboard will have a processor socket designed for a certain pin-layout etc. These vary between AMD and Intel, and also processor types.
So firstly, you'll have to stick with AMD.
Secondly, the board will have an older socket, being a Duron 900, so you are limited to processors in that range. It might be possible to upgrade it to say a Duron 1.2ghz, but you would have to get it off eBay, as they are not still in production.
So really, you can't upgrade it to anything that powerful, but if you really are set on upgrading it, I guess it would be possible to find another Duron which would fit.
If you do want more info, google and install a program called CPU-Z. Its free, and will tell you what socket your board has.

-Paul

Thanks for the Info. I think it probably means a new PC. Regards JP