Cannot connect to some servers.

I have a small network which has a Windows 2000 Server and 4 Windows XP
clients which are all behind a WRT54G v6 router. I have DHCP and DNS being
handled on the Windows 2000 Server and have it disabled on the router. For
some reason when I go to some websites (www.adobe.com is one of them) I
cannot seem to to not be able to contact some servers on the clients but I
can connect on the Windows 2000 Server.
I have tried connecting using IE7, Firefox and even used telnet like this:

telnet www.adobe.com 80
telnet 192.150.18.60 80 (192.150.18.60 is what www.adobe.com resolves too.)

However I can connect using each of these approaches using the Windows 2000
Server.
I have tried lowing the MTU as low as 576 on the client machine and the
router but that doesn’t seem to work. It seems the packets my computer are
sending may be too large for some routers when trying to connect to
www.adobe.com, however this router cannot send ICMP response back telling my
computer this (ICMP Type 3 Code 4 message).

I'm not sure why this is happening? Maybe my router is dropping the packet
but I don't see any options to prevent this? If anyone can help I would
appreciate this.

Thanks,
BravesCharm