renee,
You said that the Mac was having no problem connecting. Do you have any firewalls or anti-virus running on the PCs? If so that could be part of your problem. Also, try going to the command prompt and pinging the unit using the steps as follows:
Note: Since your Mac can connect to the device I would suggest recording the IP address of the NAS before performing these steps.
1. Click on Start>Run (for XP) Start (on Vista)
2. Type in "cmd" (minus the quotes) in the Run line (or where it says "Start Search" just above the Start button in Vista) and press Enter
3. A black window should come up. Type in "ping [IP address you acquired from the connected computer]" minus the quotes and brackets.
4. Press Enter and you should see a series of packets sent out to the NAS. If they do not return a response (i.e. a message stating "Request timed out." ) then I would suggest checking your firewalls.
5. If you get a successful ping then the device should be accessible and I would refer here for further instructions.
I hope you find this information helpful.
Message Edited by Dustrega on 01-26-2009 05:20 PM