I've never had any problem with repairing an XP install.  I've replaced many motherboards with entirely different chipsets (several SiS -> nForce) and an install repair has no problems, because it's actually reinstalling windows; it just keeps your settings and programs.  On a side note, if you're upgrading from XP SP1 to SP2, by far the best solution is to do an install repair with a slipstreamed XP SP2 disc.  I've seen several problems with just running the SP2 patch.
Just boot to the XP disc and say you want to install (don't try to repair on the 1st screen).  It will then say it found a copy of Windows already on your machine and ask if you want to repair that.  That's where you say repair.  It will look like it's totally reinstalling XP, but then when it's done you will still have all your programs.