Question : DNS issue or something else?

Thanks in advance to everyone who takes the time to even read this.

I have a problem that I've been unable to track down and it's about to make me pull my hair out.

First, the setup:
A Windows 2000 server with about 15 workstations (all with XP). The server is the primary AD controller and has DNS installed. All workstations DNS point to the server only. The LAN connect to the Internet via a cable modem. There is a Cisco router/firewall between the modem and the network. I'm pretty sure it's not the router, since I've gone so far as to bypass it completely to eliminate it and the problem persisted.

Now, the problem:
Some websites are unavailable from all workstations. The browser appears to trying to load the page, but eventually, a "problem loading page" error occurs. The strange thing is, the number of inaccessible sites seems to be growing.

I've gone as far as reinstalling DNS which didn't seem to help. I'd be very grateful for assistance with this problem. Thanks!

Answer : DNS issue or something else?

This isn't dns because you are resolving names.  You may have a router that is dying or your cable modem.  Does this happen from all machines or just a specific one?  is the 192.168.0.254 you router ip?