ISOzapp started out as a theme for BitchX 67-75pX (don't remember exactly which version, it was ages ago). Then I ported it to BitchX 1.0.
Then I realized BitchX sucks and Irssi rules.
So I ported it to Irssi, and here it is...
Diff to apply to your config file (Note: It's not fully working with the current versions of Irssi, beware): config.diff (apply with: patch -p0 < config.diff)
The actual theme file...
If you really want the BX versions, here they are: For 75pX and for BX 1.0. Note that they are not maintained and may suck.