Alex: If your buddy is concerned about running OS X on his "old" dual-processor G4, he might take a hint from Tiger's performance on your single-processor Powerbook. If that doesn't convince him it would be OK, point out to him that since his PowerMac is dual-bootable, there's no reason he'd have to "switch" to OS X at all: he could have both OSes installed, and boot into whichever one he likes at any time. That's exactly how I overcame my strong aversion to OS X over a period of six or eight months, finally becoming a Panther convert.
In reading over your Tiger license agreement, you may have missed the fact that a single-user license (assuming that's what you have) doesn't permit you to give away copies of the software, even for "trial" purposes.
Apple has a $9.95 Media Exchange Program for Tiger buyers who need the software on CDs instead of DVDs. Go to the Apple Store page, scroll down and click on "Mac OS X Tiger" in the left sidebar, and on the resulting page, scroll down below "Hardware Requirements" to "Tiger order information" at the bottom of the right sidebar. That opens a Tiger FAQ page, and at the top of the right column on it is info about the media exchange program. So when your friend orders his/her own copy of Tiger (not necessarily from the Apple Store, BTW), s/he'll be able to swap the DVD installer set for a CD set. If s/he is in no hurry to install Tiger anyway, the short extra delay in obtaining usable media shouldn't be much of an annoyance.
EDIT: Don beat me to the punch -- as usual!
