When you say, "Re-Building" what do you mean? Like, did you pull those parts from an existing system (say...a Dell or HP?). If so, then you won't be able to overclock it because Dell purposely locks the overclocking features.
If not, then I'm not sure. I've never overclocked a P4. As far as I know though, they seem to get pretty hot. I've got a 3.0 P4 with HT and it get can pretty hot by itself. And even if you could overclock it, I'm not sure you could get it much higher than it already is.
I really like G.Skill RAM. You can usually get some pretty good combo deals from them. And 2GB will be fine for her if she just does the basic music, web, and word type things.