if its a manufacturers restore disc then it will more than likely wipe the drive and return the computer to factory settings.
this is ok if you back any personal files ie/ downloaded .exes, photos, docs etc you may have saved to cd or dvd. you will then need to install all the windows updates again and any other software you have installed if you have not backed then up.
for missing .dll or system files and errors related to them try this:
click 'start/run' and type 'sfc /scannow' click ok. this will search for and replace any damaged or missing system files on your computer without losing any data. normally you would be prompted to insert your windows xp cdrom but if your system came pre installed then it takes its information from the i386 folder and should not prompt you. try that first.
can you tell us what the exact problem is please? may help.