XP will run decently on as low as a 900 Mhz system. I have it on a K6-2 450 at home and it is alright, albeit slow. My desktop here is an athlon XP 2200+ and it has no qualms about running it. Back up your data, and don't worry about your programs as long as you have the original install discs (you can't just back up a program and then copy it back to the new install, it won't work), and follow the Windows XP install. Don't be afraid to do it yourself, as long as your data is backed up. Learn by doing, not paying someone else to do.. installing Win XP is cake, as it walks you through EVERYTHING. Once you have had XP for 2 weeks, you will never want to go back to the 9.x family. I got XP 3 months before it came out as a Beta rollout, and then bought it through my school, and have been a convert for a while now.
If you have any questions, feel free to message me; as I am used to helping people out and enjoy it (I am majoring in Computer Science Engineering, and am a student TA in 2 freshman level Intro to Computers courses... I have had everything from the hacker to the guy who thought a mouse was a remote... :::sighs::: )
~D.J.~