problem with windows shares

[p0ntif]

So I set up one computer with WindowsXP that I want to be able to access from sveral other computers, but not all of the computers on the network. So I can access the share from a mac, windows 98 machines, windows 2000 machines, and other windowsXP machines. However, anytime i try to drag and drop any files onto the XP share from any of the other computers, it says access denied. The account that the other computers are accessing through has read, write, and modify permissions. What am I overlooking?