Given everything Steve just said, specifically everything that comes in 
"the next version" = 10.2 --

Waite until they package 10.2 WITH the system, of course only if your 
actually buying one from Apple.  They are not doing the same thing they 
did w/ 10.1 i.e. give the update away for free.  This will be a paid for 
update.
They should be packaging 10.2 with there new systems soon so you 
shouldn't have to waite too long.

I use 10.1.5 on my Powerbook G3 (Pismo - 400MHz G3 w/ 320MB RAM) and it 
ROCKS!!
You will also definetely need to get FINK installed and running.  It's 
great.  Uses the apt-get debian package menagement system and uses it's 
own directory structure (won't mess w/ OS X at all).  There are also GNU 
curses/ncurses lib's around that I've seen ported.  Don't know the 
versions of those but if those outdated packages are a real problem that 
might be the way to go.

Also, Oroborus has a Mac OS X like scheme.  That is the window manager 
that XonX sends with XDarwin.  It's supposed to look just like OS X so 
your desktop looks the same when you jump into Xwindows (just in case 
you fella's want the look of a Mac but don't wanna move to the PPC).
:-)

Just some things I've found on my Mac OS X journy...

HTH,
sim