I have now been asked on a number of occasions if there are tools to help re-package 3rd party applications for distribution via group policy.
The main tool in question is WinINSTALL LE and is actually a 3rd party tool available on the Windows 2000 server CD that allows you to capture the changes before and after a 3rd party application install and produce an MSI.
The KB Article for this is http://support.microsoft.com/kb/257718 and provides further info on how to use the tool. However, on my travels I have come across various tools that also do the job well (and some of them are free!)
Here is a brief list:
Advanced installer (Free) http://www.advancedinstaller.com/
WinInstall (Full version) http://www.ondemandsoftware.com/msipak.asp
Installsite.org (various utils) http://www.installsite.org/pages/en/msi/admins.htm#tools
Appdeploy (Various tools) http://www.appdeploy.com/techhomes/windowsinstaller.asp
I would also be very interested in any tools and experiences you have come across along these lines.