> I thought I'd try the 1.7.3 version of ruby; I get the same result :
> running tkhello.rb eats up 100% of the CPU.  Wondering if it the Tcl/Tk
> version I have  installed....8.3.3.
>

Bummer, this sux...anyway, here is a strace will tkhello.rb is
running...the 100% CPU usage occurs, strace prints out

select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)
select(4, [3], [], [], {0, 0})          = 0 (Timeout)

Does that help????  Same result in 1.6.7, 1.6.8pre and 1.7.3 with Tcl/Tk
8.3.3