Well, I'd start with the RAM. What kind of computer is it? What kind of RAM does it have. XP will run well with 2-3 GB of RAM installed. You won't be able to do much more than web-browsing and word processing but it will do that just fine.
A 40GB hard drive is sufficient as long as you aren't hoping to store a lot of files on the hard drive. You could get an external hard drive for storage (and that way you can move it from computer to computer too).