xp help for acer desktop

hi. hope some one can help my little brother.
acer desktop had probs so got local tech to 'fix' it. he added a new hard drive (with a few annoying and unnecessary programs) and told them to 'make sure they didnt try to update windows' (the guy dint even disable auto updates). anyhow what my bro now has is a pc without full functionality of OS as GAN has obviously recognised discrepancy.
the xp disc that they have authourised key for (bundled with acer) will not reformat hard drives.
i imagine options to be:
- ignore/remove new hard drive and make old drive primary again then reformat with original disc
- purchase new xp disc - is this possible if not some kind of builder of hardware and if so where from and approx cost (vista is more readily available but dont think his system can stand the strain)
any sugestions appreciated (i have already mentioned to him that the $400 he has shelled out to this guy plus the $200 odd he is likely up for to get new xp would actually purchase a new pc these days).

 

What kind of recovery disk do you have that doesn't format the drive and actually recover the operating system? That would be the first place I'd start. Even if the hard drive was replaced, the recovery disks should work.

 

recovery disks are specific to acer i believe

 

I thought you had an Acer. I guess I don't get what the problem is.