Hi,
Yes as the one post says (and bob tried to explain out of that post), is that you must set your boot device priority in your BIOS to boot on the CDdrive first then the HDD and whatever next. Now I'm not saying you dont know anything from computers but I am just explaining in case you dont know how to set it.... And the above does just about explain it all, but here is a step by step:

1. After powering up the computer (in the very first screen that appears) press Del or F1 or F2 or whatever button tells the laptop to open the bios setup utility.
2. Now these instructions might not be the exact same as what your laptop might offer (since there are so many different bios interfaces) as options but anyway... There should be a option that says boot priority or something in that sense, then choose CD drive as the primary priority.
3. press F10 or any other shortcut key that resembles save and exit. This will restart your laptop and before booting up windows it will look in the cd drive for a bootable cd (which your windows repair disk or installation disk is) and it will start the setup.
4. Follow the instructions very very carefully since this can make you loose all of your info on your hard drive if you tell it to reformat(which i did and lost all my games and music ) but anyway.... dont press r at the first screen since that will take you to a command prompt interface and unless you worked a lot with MS-DOS, you wont understand it... ok and yeah the rest is up to you to repair the XP installation..
Best of Luck