Welcome to the community.
Well, technically it is possible to upgrade the processor on this Desktop however upgrading the same will void the hardware contracts with Dell. You can install AMD Athlon 64 Kit, 3500+, 2.2G, 512K, 62 Watt, part number DN496 as this has been tested with the system and is with compatible with it.
Let me know in case there are any other concerns. Glad to be of assistance.
Social Outreach Professional
You can reach us at http://en.community.dell.com/
Thanks & Regards
To know more about Dell’s products, services and drivers & downloads, please go to http://dell.to/YBlak6
Thanks everyone....Yes the computer is no longer in warranty. The computer is from a friend of mine with sempron processor. I have the AMD 64 3500+ from my old computer that I'm not using, I'll probably check the availability of some dual core processor. Thanks again.