The ability to Repair Internet Explorer does not exist in the version that ships with Windows XP. This feature only becomes available after you upgrade to a newer version. This is normal and has been this way since Windows 98 and IE4.
However, you can reinstall IE in Windows XP by clicking Start, Run and entering the following command:
rundll32.exe setupapi,InstallHinfSection DefaultInstall 132 %windir%\Inf\ie.inf
You will need to have your XP CD available.
Some people have problems with the command line above. A small VB Script that will execute the command for you can be downloaded here. Save the file to your hard drive and double click it to run IE Setup.
How to Reinstall or Repair Internet Explorer and Outlook Express in Windows XP (Q318378)