monktian,
I think you possibly did not understand davidiwharper's suggestion.
Using your netbootdisk, try to access a share ON one of your Windows XP machines. (From the workstation running the netbootdisk try to map a share on another WORKSTATION instead of on the server.) If this will work you know the problem is possibly a server setting. If it does not work you need to look at your netbootdisk environment. (you need to be sure any firewalls are turned off on the workstation when you perform this test.)