I installed Apple Remote Desktop on a Mac OS X 10.1 server and the Apple Remote Desktop client on some iMacs. When Software Update offered an updated version of Apple Remote Desktop, I took the bait and updated, only to find that the new version did not run correctly. To back it out, I had to find and remove all remnants of Apple Remote Desktop's new version so I could reinstall the older version. (Sorry, I forgot the version numbers involved.) I found that if I missed any files, the old version's installer would insist that I was doing an update and fail to install.
In addition to finding files to remove by searching for the word REMOTE, I found that I had to search for ARD, the abbreviation for "Apple Remote Desktop".
Finally, I had to remove ARD-related files in System:Library:Receipts.
I hope this helps.