Are we talking about a sysprepped image or a simple ghosted image?
USB support is native from XP onwards and I've not personally experienced any issues with machines running XP using USB keyboard and mice instead of their PS/2 originals, without needing any additional drivers.
Assuming your specific models of DELL machine don't have weird chipsets that need explicit drivers for USB, then your problems would imply something amiss in the actual operating system.
You can easily extract the device PNP ID's for the USB devices either from device manager or by using one of the scripts in the articles forum (search on
pnpentity )
Once you have found the PNP id's, search the O/S for INF files and look for the PNP ids in these files.
If it cannot be found, then that may well be the cause of the issue.