I'd say it depends what you are doing with your PC..
Using Word etc, it won't really make any difference at all..
Read into all the posts about Duron based systems - it's not always a simple transplant there are a LOT of people out there with many problems getting a Duron based system to run.
If your get an easy one you will be very pleased with the result for the cost..
Otherwise - you'll be really p*ssed off!