different backgrounds on different macs,any ideas?

Hi, I am running a mixed enviroment of 10.2 and 10.3 clients and an xserve running 10.3. For some time now, even before upgrading to 10.3 server i have had a problem that if a user logs into one mac and changes their desktop image of their network home folder, then moves to another mac and changes the destop image again, every time they log in it will be hit and miss which desktop image they have! I have not found if its any other prefs that are doing this or just the desktop, but its very odd. Any files left on the desktop stay the same whatever machine is logged onto. any ideas?