shoein that's not a bad price at all for that comp,from what you said it should do you fine for everything,and later you will probably be able to upgrade it,do you have a link for it?
Sempron is built to replace Athlon XP (socket 462 and socket 754) and, and also a cheaper non 64 version of the Athlon 64 (socket 939). Honestly, if all your doing is downloading and surfing the net, go for a a cheap system but think about getting more ram. For what you plan to do ram will be one of the most important aspects.
My sister is running a PII 350 with 256mb ram for downloading and surfing the net.
I would recommend 512mb ram. Thanks just my opinion.