Actually, the 350 is kind of an exception to the firewire rule. It is a slot loading imac. It just doesn't have firewire as a cheapo version that was for sale at the same time as the 400 sl imacs. You should be able to install tiger without xpostfacto. Search the threads, people have done it.
Hmm, really? That's not what i've heard before, but i'll take your word for it. I finished installing the 10.4 already with Xpostfacto and the iMac is running happily it right now