I found Tor works with privoxy but not the recommended polipo on Ubuntu 9.10. To run tor first add the following to /etc/apt/sources.list:

deb http://deb.torproject.org/torproject.org [distribution] main

Now install Tor and the proxy server with:

1. sudo aptitude install tor privoxy
2. sudo vim /etc/tor/torrc and modifyMaxCircuitDirtiness
3. sudo vim /etc/privoxy/config
4. comment out: logfile logfile
5. find: listen-address 127.0.0.1:8118
6. add (on next line): forward-socks4a / localhost:9050 . (including the period)
7. sudo /etc/init.d/tor restart && sudo /etc/init.d/privoxy restart

Now set 127.0.0.1:8118 as proxy (eg in firefox) to access the Tor network.