How many channels of multitrack audio recording?

40MB/minute is less than 1MB/second. Even the slowest laptop hard drives have no problem writing many times that per second. So yes, the PowerBook can easily keep up with 8 simultaneous channels, and there is no reason it should glitch out over long time periods as long as you are not multitasking. What you are asking of your PowerBook is not exactly the most demanding thing in the world. Now, if you want to apply real-time effects to each of those channels, then that might be a different story...

Really, it's impossible to predict in your specific setup without testing. In theory it should work. In practice, it depends on way too many things including the stability and version of your particular OS and software load, the software you run to do the capture, the fw audio interface, how fragmented your drive is, whether you are using software effects like compression or EQ on the inputs, etc etc

You're best bet is to test it thouroughly first, and go in with a backup plan ready. Personally, if this was a live event, I would probably rent or buy an ADAT or Tascam DA-88 DTR to run in tandem with the computer. Have extras of everything: mics, cables, tapes, external hard drive, everything.

Given that you have the inputs on your interface, 8 channels of simultaneous recording is well within the capabilities of the processor, however, it's not a good idea to capture contiguous audio (or video) to the system drive as OSX (UNIX) writes to the system on a continuous basis and that can interrupt the recording.

Your best bet is to invest in an external drive, one of the 7200rpm LaCie's is a good bet, although you only have FW400 on your PB, shouldn't be a problem though.

Most software will allow you to specify how long you wish to record for in one shot, Protools, for instance, defaults to 30 mins. This is to prevent accidentally filling a drive up with silence.

You can change the default obviously.

I'm not very experienced with Mac's, so this could all be taken with a grain of salt... however, I would think that your powerbook might be ale to perform your maximum task, but you'd be on the very edge of the hardware's capabilities.

First of all, laptop hard drives are by no means the fastest. Although I understand you want to avoid the extra hardware, an external drive has so many benefits, you might regret not usng it. Faster speed (even through the Firewire), seperate from the os, etc. If you choose to get one, try to pick one with at least an 8MB buffer - it'll help with the heavy burst mode loads, should the drive become fragmented.

Second, make sure you're loaded up on memory. The software will attempt to buffer the incoming audio on it's way to the hard drive, and you'll want to minimize virtual memory (or swap file - I dunno the mac terminology yet) hits in the process. If there are too many of these hits, it's almost as if the hard drive has to record the incoming data twice, which significantly hampers the process.

Third, as was stated above, fragmentation of the target drive makes a big difference. Try to keep your drive clean and organized - your audio will thank you.

All the advice given above is excellent, and as I said, I'm no expert Mac user. however, one of the reasons I switched was for the increased perfornamce with audio / video across the board. My Sony Vaio k23 has recorded 4 tracks while playing 8 - a limitation of my input device. i did this using USB and the laptop's internal hard drive, and I was pushing the envelope. A powerbook should be able to exceed that envelope, I would think, and your equipment seems up to the task. Just be sure to take the steps necessary to ensure the best possible experience, and you should be fine.