Reverse Proxy on Windows

I'm trying to circumvent a corporate proxy solution to access Webmail by
building a reverse proxy on a server behind my broadband firewall.

I've had limited success with Apache, in that I can get the server to
reverse-proxy the front-page of my e-mail service using the following
commands:

ProxyPass /fm http://www.fastmail.fm
ProxyPassReverse /fm http://www.fastmail.fm

My problem is that when I log-in, my browser is redirected to the real URL,
rather than that of my reverse proxy, which I thought the ProxyPassReverse
directive was for.

Can anyone point me in the direction of an alternate product. I'd also
welcome feedback on the above.

Cheers,
Chris