Any special tool for testing a web chat application?

[Barry Archer <archerba () gmail com>]

I need to test a web chat application.

I was wondering if there's any recommendations on a special tool
and/or approach that might be the best.

Right now I'm looking at:
  Nessus
  A full web application scanner (HP/SPI,AppsScan,or Cenzic)
  A proxy for manual testing (WebScarab, Paros, etc)

 Sorry if this is a silly question, but chat seems like it's smaller
in scope but harder for that initial automated scan.

Thanks

   Ba