Problem networking Access database

Not sure if this is the right newsgroup, but I hope someone can help.

Main machine containing my databases runs Office XP on windows 7.

On another machine (Office XP with Windows XP), I can open any other file
type on the main machine, but when trying to open a database, I get the
'Can't open - file not on intranet or in a trusted location' message. I
have Windows Security running.

As far as I know, I've set up the workgroup correctly on both stations -
shouldn't this allow me to freely open files?

Very grateful if someone could point the way.

Ian King