Backup all your files. Make bunch of CD, DVDs so you won't regret it later!
Restart your computer, and keep key down to enter BIOS (for Acer I think is F2 key).
Search the BIOS for BOOT DEVICE , FIRST BOOT DEVICE or something similar.
Change it to your cd rom drive.Save and exit. It will restart and the cd will load.
Ok, here's how I do it:
I usually choose recovery console and format my drive from there( if you know how to use cmd)
Press r for recovery console/repair.
Chose Windows instalation , usually 1 and press enter, and put your password (if you don't have one just press enter)
Type cd C:\ and then press enter
Type format C:\ /Q (fast format) and press enter.
But you can also choose your type (FAT32,NTFS) if you want, by format C:\ /FS:FAT32 /Q or format C:\ /FS:FAT32 /Q
If you get a confirmation then you formated the drive.
You can check it by typing cd C:\ and then type dir. If there are no files then it's clean.
Type exit or just restart.
Wait for windows to load setup
Choose To set up xp...,agree EULA (F8)
Choose To set up fresh copy....
Choose partition...bla, bla, bla....
Good luck!