This is a very simple application that when run, easily allows you to load up the system or user PATH environment variable, edit it, then save it back.
Not only does it provide a multi-line textbox for editing the paths all in one long string, it also provides a nice grid for easily editing individual paths.
Check out the source code and downloads!
Also, for those of you who are interested in such ui-candy type-of-things, take a look at how the folder browser works; It will maintain environment variables in the paths! Nice, right!?