First of all, extract ReGen200.umod to a folder (make sure there are no spaces in the path name).
Then, just double-click on ReGen200.umod to install. In the "install to" field enter your base UT directory. Eg. C:\Games\UnrealTournament. Then just follow the on-screen instructions. 
If when you double-click on the umod it does nothing then setup.exe is not setup right in your UT directory. You can assign umods to the setup file in folder properties, or click on the "Start Button", then "Run..." and type this:

[Unreal Tournament Dir]\System\Setup.exe install "ReGen200.umod" 

Alternatively, you can download a nifty utility called UMOD Tool, available from Unreal Services which will do it all for you!

The full ReGen readme will be installed to your ...\UnrealTournament\Help directory.