Internet sharing xp/vista

I can't find anything in the discussion groups so I'm posting a question. If
its been dealt with, just point me in the right direction. I have two
problems, which may or may not be related.

1) I am running Vista with a dialup connection (all that's available). When
I first set up the machine, I was able to connect through ICS from my other
machine (running XP Home -- with SP2). Now, while I get a tray icon showing
the internet connection is enabled, the xp machine cannot connect nor can it
ping any public address. The status dialog is contiually updated, showing
large amounts of both inbound and outbound traffic, but now, unlike when ICS
was functioning normally, it does not show speed of connection.

2) The dial up connection from the Vista machine never gets better than 26.4
K. When I disable ICS, and connect directly to my ISP with the XP machine it
typically connects at about 36-44 K.

I've run through network setup a number of times, including trying to make
the XP machine the host, but not succeeded in getting ICS to work. File and
print sharing works perfectly.

Any suggestions would be appreciated.