Put the files
DeployableFun.u
DeployableFun.int
DeployableFun.ini
into the 'System' folder within your 'UT2004' directory and you're done. After a restart of the server the mutator should appear in the mutator list of the WebAdmin interface.
In addition you can force players to download the appropriate files when accessing your server. Open your server's ini file and search for the string 'ServerPackages='. After the last such entry add the line
ServerPackages=DeployableFun
If there are any questions left, let me know.
EDIT: although it's just a minor change: it's always a good idea to backup your ini file first