which mac for lightwave

ok, i've never used lightwave before, but some of the classes i'm taking at school next year will heavily depend on it, so i'll need to use it at home. however, i've noticed from the system requirements that my 1.25ghz emac will get eaten alive by it! so i need to get a new mac. i'm still not sure how much money i'll have to spend on it, but it's going to have at least 1.5gb of ram i'm pretty sure, if y'all think that will suffice. the two machines i've been considering are a 20" iMac or a 15" powerbook with the vram upgrade. obviously the powerbook won't perform as well, and it has nowhere the screen real estate and will cost significantly more, but i'd really like the portability. would i miss the power? the screen size? i've also thought about a 17" pb but that'd probably cost too much. a powermac's pretty much out of the question as far as price unless i get a refurb. should i get a refurb? sorry about all the questions...just sort of worried about getting a sufficient mac. i'll probably be buying late july-early august. also, if you think i'd be better of with a pc, i guess i could possibly switch back...

thanks in advance
alex​