Backing Up

I am a Part time IT guy at a real estate management corprate office.
They own about 20-25 apartments that we have managers at that do their
own thing there and have important word docs, excel spreadsheets just
stuff like that. We run a Windows Server 2003 SBS at the office that
the users their put it all on a shared public drive that is in the
Server PC and then that gets backed up on a tape. They all run Windows
XP Home edition but i think a few have Pro but......

I just need some advice on what i can do to backup their pcs without
going to the apartments everyday and do a backup. USB Flash drives for
all the properties maybe? If anyone has a good idea on what i can do to
backup all of their PC's please let me know. Thank You!

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