Dell Deminsion 2400 Upgrade Questions

My biggest question is what is the fastest/most powerful CPU I can put into this motherboard?

Second question is, basiclaly the same as above, except RAM.


I'm trying to help my younger sister upgrade her computer, I don't have access to the machine in order to open it & get any thing extremly specific. I know the RAM was switched from it's 512MB stick to a GB stick. BUt that's all I know, everything else should be the same as how it ships from Dell.

I am able to "remote control" the computer, so if you need any information that I didn't list but able to get by remoting into it, let me know.

EDIT:
Obviously there is a budget, unfortunately I don't know what that is. I haven't asked them and just trying to see what the ballpark price will be so I can let her know that way.