No OS is technically "crash proof", Unix - the heart Unix, even crashes, but thats just because of faulty everything. Nothing's perfect, but Mac's are most stable than Windoze. I installed WinXP for the 10th time 2 weeks ago and its crashed 5 times so far. I bought this iBook and put tiger on it about 2 months ago and no system crashes or kernel panics. Just a few program crashes (but that was due to it being 3rd party software from never heard of companies (like Adium X, Snes9x)). Other than that, no programs have crashed on me yet.
EDIT: Welcome to the forums, hope your purchase a Mac soon - if you don't have one already. We're always here to help and if you need specific help you can post here or contact me directly.