In win xp :
when you install win xp after few moment it show a page with repair. pass this page when a another page show with repair (2nd time) then you repair your windows.
so you don't need to reinstall other thing.
Is it possible to reinstall windows without re-installing everything else?
Yes it is, ill explain how!
1) First backup your data just in case, for this i recommend Dmailer Backup because its free and will grab all files even the one you have forgotten about.
-Download it from http://www.dmailer.com
-put it on a portable storage device and run it
-select the files types you want and let it do the rest.
2) Get your windows cd insert it into your computer then restart windows.
3) When you computer is booting it will do one of the following.
-launch the cd automatically (Note: if you do this you will have to eject the cd after the first part of the installation)
-ask you to press a key to launch the cd (if so press any key)
-Or if nothing, then you need to restart your computer and enter the bios normally by pressing DEL or F2, then in the bios change you boot order to either ask you or boot to cd. (Note: if you do this you will have to eject the cd after the first part of the installation)
4) After launching the cd the first option you get is to repair you dont want to do this as it is in fact recovery console to a windows repair. You want to continue as if you where reinstalling windows.
5) VERY IMPORTANT, when you arrive at the format disk page you want to select the option... Keep my current file system intact. this is very important if you format you will erase all data.
Because you have selected this option windows will reinstall itself over you old windows giving it a fresh start.
6) follow the rest of the configuration to finish the install. ( This will end the first part mentioned above. Your computer will reboot if you see the same steps come up again eject the cd and restart your computer)
Note: i recommend you backup everything with Dmailer Backup then format you disk, i don this at least once a year to improve performance there is nothing like a fresh OS install.