Allright... a little update for anyone who cares.. I'm just so excited to have this thing up and running lol.

The corrupted filesystem seems to be due to EXT4. So that may be worth concidering if you want to dual boot with ubuntu. You may wanna use EXT3 as it is probably the safe bet.

The complaining about CD drive error was not really the CD at all but just my secondary HDD that I hadn't partitioned yet. So now that it's done it workes fine. Tried to make a backup with time machine to the secondary hdd but that actually caused OSX to crash in the middle of it. Seems a little worrying, I hope I won't get this with other things too.

Anyway, I'm starting to feel most things are working fine now. Thanks again snow for the excellent guide!