The main technical skill currently  required of a Swarm user is the ability to write in at least one of following object oriented languages: Java or Objective C. Other recommended skills include the ability to use tools such as gdb and emacs. For the record, if you know C and have some form of experience in either C++ or Smalltalk, then learning Objective C should take no more than a day or so.
Here are some Objective C resources:
Objective C references List of Objective C references on the Web. Includes a 10 minute overview to Objective C that is most of what you need to know about Objective C. Originally contributed by Nelson Minar
Object-Oriented Programming and the Objective-C Language An excellent (online!) book on Objective C. This is for generic NeXT Objective C: Swarm uses GNU Objective C in addition to our defobj extensions (see defobj library in : Reference Guide to Swarm)
Unlike Objective C, the market is literally bursting at the seams with books on Java, so we merely point out a few relevant sites:
As we continue extend Swarm's multilanguage features, further language bindings may become available.