Alright so I've followed the following steps:
1) Rooted phone - worked
2) Rebooted into clockwork recovery - worked
3) followed the instructions here http://wiki.cyanogenmod.com/wiki/Sam...l_Update_Guide
The end result was that after it said it was done installing the cyanogenmod rom, it rebooted annnnnd... nothing. It's just sitting there with a "Samsung Galaxy S2 GTI9100" logo with the yellow warning exclamation. I'm not sure what to do at this point - I can put the phone into download mode, and odin can still connect to it, but that's basically it. I'd really appreciate any help with this.
UPDATE: I've managed to get into the recovery menu using VOLUMEUP+HOME+POWER, but when attempt to repeat the operation of wipe,wipe cache, install from sdcard I get up to installing from sd card and then I get:
Opening update package...
assert failed: getprop("ro.product.device") == "galaxys2" || (etc)
E:Error in /sdcard/update-cm-7.1.0-GalaxyS2-signed.zip