On the Dell and Compaq, where they or are they PCs from work -- provided by their IT staff? If not, than they should be able to log on to either HP.com for the Compaq or dell. com for the Dell to purchase the restore CDs from the OEM manufacturer.
These are usually priced fairly. The answer my friend is "call support."
Oh yeah -- if these are work PCs, then the IT staff may have placed a corporate image on them and destroyed the restore CDs intentionally. Either way, "call support" for help getting those restore CDs.