Ok now I'm really reaching on this one (while waiting for the O/P to tell us what model/brand of computer we are dealing with).If it is as stated"the computer is pretty old" then is it possible that the original O/S was NOT XP but W98?
It's quite certain, actually... Well, either that, or it came with W2K.
If so and the O/P has the access would it help anything to do a double boot with win98 as the other O/S.Then see if the USB ports will show up in the Win98 configuration.
It could eliminate my unlikely theory that Windows XP purposely disabled them. I highly doubt that is the case... also, this would mean they need a windows 98 Disc.
Or will that have no affect on the fact that the Host Controllers are not present? Please don't laugh if this is ridiculous --just say so i can take it. 
truenorth
I'm going to have to say, it's very strange that the Host Controllers essentially don't exist. I'd like to revise my "theory" based on the new evidence (specifically, that PC Wizard 2010 states USB Bus:No).
If there is, without a doubt, no USB setting in the BIOS. Then except in the rare case where such an option is enabled/disabled through a jumper, there very well may not be any USB functionality. Sure, it could have the header block installed, but unless it's plugged into a USB header, it's not going to do much.
But I don't think this is very likely. Most motherboards since 1996 have at least USB 1.1 built in. It could be a hardware problem- but then the options would be in the BIOS screen. A most curious issue this is.
