0xTWT is the only* Twitter client that is specifically built for PowerPC Macintoshes. 0xTWT also gives some love to old Power PC machines. You don't need a G5 to run 0xTWT.
*at least the only I know of
You don't need a G5 just for some 140-character action. 0xTWT is built to run on slow PowerPC as-well as on a Quad G5.
And the best is: You don't have to rob a bank!