VPN packet filtering

I have a client that randomly connectes to a VPN server over a point to point
T1 for email and internet access. Typoically this client is used to stream
multicast data to other machines. When the VPN tunnel is invoked, the
multicast data is mistakenly encapsulated and sent across the T1. How can I
stop the multicast traffic from traversing the T1 through the VPN. I'm using
pptp and w2k3 server.

I've looked at using pptp filters through Remote Access Policies to no
avail. It doesn't even seem to block anything when I set the filter to block
all packets. My users are defined to use Remote Access Policies in the dial
in tab.

Thanks for your help.

TJ