The easiest way to contact me is via e-mail. My primary address is andrewho [at] andrewho [dot] co [dot] uk. For those in the know, my PGP key (F4F983CE) is available on all decent keyservers; a local copy is also stored here.
I’m very rarely on IM, but when I am it’s andrewlkho@jabber.org via the XMPP protocol (Jabber / Google Talk) or andrewho [at] andrewho [dot] co [dot] uk on MSN Messenger. Be warned, though, that the likelihood of me actually being signed in is fairly close to zero.