multitracking in Cubase 4 -- HELP !!

Hey sorry if this is the wrong place for this but I’m not sure where to jump in. Please advise or let me know if you can help. Thanks

Ok. Trying to record some nice tracks of the band during rehearsal. I’m running a MacBookPro 3.06GHz Intel Core 2 Duo/ 4GB RAM / internal 500GB @ 7200RPM external 2TB
FW800 @ 7200RPM.

Recording @ 44.1 / 16bit

I’ve been recording in Cubase for years but never tried multitracking 18 channels at once.
The first 2 song recordings went fine but then I got a message saying I did not have the room left? I notice that as I activate record on each track the Record Time number in the bottom of the tracking window decreases from about 3000hrs to 280 or so. Am I missing something here? I should surely be able to do this. Even if I had to dump everything from my drive before each session.

Please help. I hate not knowing.