Tor + Firefox
I recommend to start with the Vidalia Bundle. There Tor comes with a graphical control centre + Tor button for Firefox. the Tor button is a plugin that allows you with 1 click to turn on/off the Tor routing for Firefox.
Tor + Bitcoin
using Bitcoin with Tor is easy. All you need is to check the proxy option. The predefined values in Bitcoin match the Tor settings. As Bitcoin only saves from & to addresses (and no IP addresses), you should be pretty safe. Tor however does not fix the traceability of BTC from one address to other.
Tor + IRC (mIRC)
This is worked for me on two different computers, drop me a message on Bitcoin forum if you need help.
some user started creating a tor page under his user space: https://en.bitcoin.it/wiki/User:Sawzall/Tor
maybe there's some stuff you guys can pull in from there...
also, xchat instructions for using over tor can be nice to have too. not everyone uses mirc, you know. :)