Odd RRAS Problem - Server 2003 SP2

I have a Windows 2003 server running RRAS servicing a few client
computers. It has DHCP, DNS, AD, IIS, and MSSQL installed.
Yesterday, for no apparent reason, it stopped routing certain packets
from my client computers. Topology of the network:

Clients - Vista Machine/XP Machine/XBox 360

go to

Server - Windows 2003

routes to

Cable Modem

I've verified the internet connection, and the cable modem. The
server can browse the web and functions normally. The Vista and XP
machines are without Web/Chat access. Whats odd, though, is that the
XBox 360 can connect to XBox Live! without problems. And the two
client computers can ping external domains. So network connectivity
is there, and my pings are being routed, but I can't use any other
services.

I did a packet capture and did web requests to google. When using the
server, the TCP connection request immeadiately responded and I was
connected. When using the Vista desktop to connect to the exact same
IP, the TCP request just timed out. The only differences between the
two packets are:

1. Sequence Number (Expected)
2. Time To Live (The desktops TTL was 127, servers was 128 - Expected)
3. Checksum (Expected)
4. The Vista machine had the Window Scaling TCP option included, which
extended the length of the packet 4 bytes.

Other then that, everything was completely identical. Although I
didn't packet capture it, the XP machine doesn't have any web access
either. I've started and shutdown RRAS, reinstalled RRAS, and
rebooted the server. I've also gone through all of the RRAS logs (The
ones in %windir%/Tracing enabled by changing /EnableConsoleTracing
registry key) and found nothing. At the time the router stopped
working, NONE of the logs show any odd activity. After a few hours of
looking at the logs I've found that nothing seems to be out of place.

I can also access the cable modem from the client computers, using
it's address of 192.168.100.1. My packets are getting through,
somehow. I'm really stumped on this one. Is there anything that RRAS
does that disallows certain types of protocols? Is the ping command
doing some funky server thing where it's simply relayed by the server
instead of routing? Thanks in advance,

David