I realize it's not meant to be some dream PC, but just get nice parts now so you don't end up wasting money later. My main suggestions:
Hard drive: just go with SATA and 160GB+ (200GB is best)
Monitor: Definitely get 19", not a lot more expensive and SO much more room!
Processor: Celerons... eugh. I don't want to start a AMD vs. Intel war, but look at AMD/AMD mobo...
My main thought with this computer is that you could buy a cheap dell with as many features, if not more, for the same or lesser price.
Check this thing out:
It costs $300 less and has XP already installed. The only thing you would need is a monitor...
I realize it's great to build computers and to have the full control, but Dell can be really nice and reliable if you're just looking for some multitasking.
Otherwise looks perfect for what you're looking for