Hmm, any reason I'd be unable to use 'irb/completion' out of the box in 
1.8.2-preview2 ?

It likewise ignores the request to use it in my .irbrc

[mccallister@kite ~/src/eva]$ /usr/local/ruby-1.8.2-preview2/bin/irb
irb(main):001:0> require 'irb/completion'
=> false

[mccallister@kite ~/src/eva]$ ruby -v
ruby 1.8.2 (2004-07-29) [powerpc-darwin7.5.0]

[mccallister@kite ~/src/eva]$ uname -a
Darwin kite.forthill.int 7.5.0 Darwin Kernel Version 7.5.0: Thu Aug  5 
19:26:16 PDT 2004; root:xnu/xnu-517.7.21.obj~3/RELEASE_PPC  Power 
Macintosh powerpc

-Brian