Slow network saving and office 2003 opening/saving

Hi

I have a small customer who has 5 computers on a network, the customer uses one pc as a file server/ reception pc.
The customer is reporting that some parts of Office 2003 are slowing opening files and queries.
Secondly when other uses are saving files to the computer it has a long lag.
The system is a core 2 duo, xp and 3gb ram.

Any advice would be great.