Formatting windows xp 2002

Hello, my problem is, i have just had a pc given and it is very slow, the screen keeps freezing all the time. it also takes ages to load any web page i go to. i have went to format my hard drive and it says my computer is "healthy" will this be true...? as its givin me these problems i.e.screen freezes and takes ages to load anything. if i need to format my hard drive..! what programs will i need to bak up on to c.d. so i can reinstall them..? i dont no how to format a hard drive, im just going off wat im googlen, i keep reading that i will need to back up programs but dont no what programs to back up and how to bak them up. im exelent at following instructions as long as they are clear. i will look forward to your advice and thanks to who ever helps me with these problems.. thanks Rob