PCX Plugin allows you to import, edit, and export .pcx files.
Edit by : PCX Plugin, a Paint.NET, allows you to import, edit, and export .pcx files.

updates:
A user kindly reported that the plug-in seemed to bloat the sizes of files on save (e.g. load a 16k image, save it at 300k). I investigated and it turned out that my code had a flaw such that compression would never occur. Oops. (Serves me right for wanting more of a file loader than a file saver.) you can free download PCX Plugin 0.9.3.0 now.