Help! Need help writing a batch file

OK - so the powers that be decided to upgrade a program which was installed system wide at many different site, but to do that the old program has to be manually removed and the new version manually installed. Our IS tells us this is the only way for some reason.

What I want to do is write a batch file that I can set to run at start up, or at least run the batch file on each machine so that running the script will:
1. Uninstall the original program with all associated registries
2. Install the new program

Unfortunatly I can't find an uninstall.exe file. Is there a way I can run a command to prompt the windows uninstall sheild to remove a specific program, and then place that command in my batch file?