You have way too little RAM for XP. The minimum for reasonably good performance is 512MB, but 1GB or more would be much better. Was this originally a Windows 98 machine?
"I've had to reinstal windows on several occasions before this"
This is generally a sign that a person doesn't know how to fix a problem.
"If I could just find out how to format the hard drive"
It's all done with the XP disc - boot off the disc & watch for "Press any key to boot from CD...", press a key & wait for Windows setup to begin. From there, all you need to do is read what's on the screen & do as it says. Partitioning & formating the drive are all part of the process. This site will walk you thru it: