Help! Install problem; simple solution?

[deleteme]

Just installed Squeeze (debian-6.0.4-powerpc-netinst.iso) on a working 
New World iBook G3, and everything went smoothly until the first boot up 
of the new system. After displaying the typical sequence of line-by-line 
boot progress, the log-in screen was presented to me in a completely 
jumbled fashion. It is unreadable, though presumably it is asking for my 
username and password. No hardware problem is suspected.

Now I'm stuck because I can't ascertain what the problem is, and I won't 
be able to use any advice like "type this, click that, execute 
such-and-such." Probably everything is working except this screen 
glitch. What happened? What can I do? Is there a known fix without a lot 
of "try this, try that" guesswork?

Thanks,
--Rob