Intrastate connection

The place I work at has offices in different states. There is interest in setting up something so that information (actual computer files) can be accessible from either office.

There is no domain set up at either office.

Most of the computers here are running XP Pro SP2, except some WinME machines. And there are some machines running Win2000 and Win98 at the other office.

They want the connection to be exclusively internal, and do not want the Internet to be used in any way.

Any ideas if this is possible?

Thanks