Actually, IE on Vista is supported...well, at least version 7. The problem was that On IE7, it is TLS which seems to be turned on by default on 7 but off on 6.
Also, I had the following and removed "ssl advanced-options sslparams" and it worked.
parameter-map type ssl sslparams
version SSL3
ssl-proxy service sslproxy
ssl advanced-options sslparams