RAM is definitely important. On a mac for performance judging from what i've heard and seen of my friends tibook g4 gig RAM, you need a gig of RAM. I will say, and it has been said before, that pcs are noticably faster and capable of considerable more tracks and effects, my tibook buddy just about cried when he saw how much my toshiba satelite p4 2.4, gig Ram, xp pro could handle compared to his much more expensive mac. That said, it seems people definitely gig on macs, and I was under the impression that 828's were well suited to macs. I've found that using a fast external firewire harddive (7,200 RPM, 8.9 ms seek time) is key to large track counts--have you Live content folder there, have your clips ther, record to the external drive. I do this while using a pcmcia RME multiface setup, which is nice since I can use my 1 firewire port for my ext drive, and my pcmcia for the RME. I've heard of, at least on pcs, problems when using multiple firewire devices (like 828 and an ext. drive). Are you using an external drive, is it firewire too?
Usb interface for audio works, but is not reccomendable if you can afford more. The bandwidth is not as good as firewire, and track count is limited. 828 is better than any usb device i can think of. Are you osx or 0s9--seems like mac users have better luck with Live on 9. Don't give up on live yet, it definitely can work on a mac without audio problems, its just a matter of figuring out what is causing the problems (have you updated to 2.0.3?). Worst case maybe try a reinstall of everything (or maybe one thing at a time like 828 drivers, then Live, and if all else fails, reinstalling the os)?
The scene situation you describe to me sounds like it is either RAM or internal (slow) hard drive related--Live is struggling to spit out all of those clips at once, which means they are too slow to load up, which in my experience seems most likely to be a hard drive thang--are you using internal? and pcmcia isn't just popular all of a sudden, if you research laptop interfaces for long, all roads lead to the RME--it's been around for awhile--and for good reason. It has zero cpu load (it does all the processing itself, not taxing you computer at all), not so on firewire devices. Despite the bs touted in an earlier post that pcmcia is only 20 Mbps, it is indeed faster than firewire, and RME is the best laptop solution for a serious and/or professional musician. I can record 16 tracks of 24/48 simultaneously at the lowest (1.5 ms) latency into Live, and playback many more than that with many a Live and vst effect.