i was just asking because i had the same issue but with service pack 2 , i cant really comment on your issue if i dont know if its the same thing , SP2 has been out a while so you most likely already have it anyway
if yuor stuck in an update loop like that and theres no safemode available then the only way out of it is a reformat there really is no other option , do you have an operating system disc (vista on dvd) a repair install could be an option , but if its anything like the problem i had with SP2 your gonna have to go the reformat route
see what your tech guys say .............. i know what there gonna say already
office tech guys really know their way aroung an office network but give them an actual pc issue and they will run for the hills