PPTP Multicast?

Hi,

I've got a private network with addresses 192.168.12.y over eth0.
Multicast works fine here. I have pptpd running assigning address
192.168.12.y (the DHCP server on eth0 assigns lower addresses than
pptpd does). What I'd like to be able to do is have multicast route
to hosts connected via PPTP. Is this possible? I feel like I
shouldn't need a multicast routing daemon, as it seems like they're
designed for complicated networks, but maybe I'm mistaken.

Just to give an idea of what's happening, right now when I ping
224.0.0.1 from hosts on eth0, I get responses from all the multicast
hosts, but if I ping 224.0.0.1 from a PPTP host, I only get a response
from the server.

I'm currently running Linux 2.4.22 and the hosts on the other side are
all running Windows XP/2000. Thanks.

Cheers,
J.