Webmin is much more than a configuration tool. It's a web-based system administration tool. Which means that one can install software, configure applications, setup hardware to some extent (i.e. create printer profiles, etc). In order for webmin to give you such control over your system, it must replace (read rewrite) some of you installed files to include code that webmin can call to do it's job.
Since you installed via rpm, let's hope that the webmin rpm is well-behaved (meaning that the packager included instructions in the rpm spec file to save a backup copy of files to be replaced before actually replacing them). The files are saved with the original name, and an extension to that name. The most common extensions are .save, .orig. and .rpmsave. The rpm spec file will only specify one of these extension.
The first thing to do, open a terminal and issue the command 'locate webmin | less'. If nothing shows up, su to root and run the command 'updatedb' to update the locatedb. Then try the first command again. Once you have updated the locatedb, look for files which may have been saved by rpm. Specifically, locate .orig, locate .rpmsave, and locate .orig. If you find a host of such files which refer to the files you're having trouble with, recovery is fairly easy, though time comsuming.
First, take note of the extension used by the webmin rpm. Then remove webmin. Now the tedious part. Locate all the files with that extension. In each directory in which you find such a file, copy or move it back to the original file name. That will restore the original file. Be careful and verify that the file you are restoring was changed by webmin (check the date/time stamps).
Once you've done that, your system should be functioning properly again. Then, if you still want webmin (it is an excellent tool, with additional modules available from the webmin site), I'd suggest that you get a .src.rpm, and build a binary specifically for your machine.