I just grabbed iTunes 4 and I'm trying to install to a 17" Powerbook. I've never had any issue with installing anything to it, but iTunes stops at the "Select a Destination" part and won't allow me to install. It says:
"Installing on this software requires 21.8MB of disk space.
You cannot install this software on this disk. (null)"
I've got nearly 44 Gigs of free space and I'm selecting the only disk available (the Powerbooks hard drive).
I've downloaded the software again with no change.
I'll restart and see if things change, but I wanted to find out if anyone else was seeing this.