Get the PowerBook!
If you can afford the PowerBook, forget about the iBook. You said you would use it for gaming; the extra 20% raw cpu speed as well as the bigger L2 cache will improve the performance of any current game title. Secondly, the iBook is, performance wise, at the bottom end of the entire product line. Everyone looking into buying a new computer should consider that it can only be a good investment if the new machine is capable of serving you well in the years to come. I seriously doubt that the iBook is a good investment for that matter. It's a great value, yes, but you get what you pay for, therefore, once again, go for the PB, not mention all the extra features such as mini-DVI monitor spanning, twice as much onboard RAM, built-in Bluetooth, better keyboard!
Edit: As for which laptop can take the beat better, definitely the iBook 'cause it was engineered for students who don't take as much care as a professional user. But you don't have to be more cautious with your PowerBook than with any other laptop, just keep in mind that it has an aluminium case and can therefore dent.
Boot time: Depending on what kind of Windows machine you are using, the PowerBook might take a bit longer to boot than a Windows machine but the wait is absolutely worthwhile as MacOS X is so much better than Windows. (Im a recent switcher, too) Just make sure you install the 10.3.3 update, it will decrease your booting time significantly.