GRUB hangs on Mac Install

[Wade Smart]

03262007 1305 GMT-6 DST

My client has a new iMac with intel core 2 duo with 1gb ram and 230gb
hd. After bragging about how great Ubuntu is he tried to install it on
his system. He gets most of the way through install but then when it
comes to booting it throws this message:
GRUB loading stage 1.5
GRUB loading, please wait...


and never gets beyond this. He said he left it for about three hours
thinking it would just get through whatever it was doing - but
apparently not. Any suggestions?

wade