I have exactly the same problem. (hangs at gagp30kx.sys) I have searched many sites posting this same error and 'potential' fixes but have not seen any that are definitive.
I am lucky enough to have the memory diagnostics, hdd diagnostics, and a spare emergency xp ghost backup. The diagnostics pick up nothing. The backup hdd, backed up 6 months ago, gives the same fault as the original xp disc. If I put this disk in my other computer it works just fine. No harware updates have been done to this machine for months. If I boot using the 'ultimate boot cd' the machine runs and passes any diagnostic I can throw at it.
