Mapping drive from Win XP to Mac server

I manage a mostly Windows network but still have to support a group in advertising using a range of Macs; iMacs, G3s, mostly. They won't let go of their old Mac server (OS 8.5). Two users in this department use Windows boxes, one is 2000 one is XP Pro. I can map a drive from the 2000 machine to the Mac server no problem but the XP machine won't go. Have tried other XP machines and got same error message:

X:\ is not accessible
The specified network name is no longer available

Anyone out there have experience mapping to a mac server from XP??