If you are frustrated by Apple's insistence on upgrading your copy of Apple Remote Desktop to run on your 10.5 machine, do the following:
Install Apple Remote Desktop 2, then install the Apple Remote Desktop Updater to v2.2. Now run Applications » Remote Desktop and enter your serial number. Remote Desktop will now give you the message that it cannot install due to a newer version. In the Finder, navigate to:
/System/Library/CoreServices/RemoteManagement
From the folder, delete (or move) the ARDAgent v3.X file. You can now run Remote Desktop 2.2 in 10.5 -- sweet!
[robg adds: I haven't tested this one, and there may be things that don't work properly using an older version of ARD in 10.5. Proceed at your own risk.]

