Hi! I'm relatively new to this forum but I've been using TCL for years, ran into the same problem as OP:
Irssi from the 4.x repo depends on libssl-0.9.8, which, works fine in tcl 6.x -- However, something has changed and the original irssi's dependence upon the perl5 library is outdated - irssi won't actually run.
I've taken the time to install the necessary dev libraries (perl5, openssl, ncurses, glib2) and recompiled it for tcl 6.x. Emailed the package to the proper email; I'm just waiting on a response.
@eminger: If you want to pm me I'll send you the tcz's for the newer build of irssi; I feel like just posting it without proper authorization would be disrespectful to the people working so hard to keep this so organized and maintained
EDIT: Should have made this clear; I actually made the extension submittable to the repo, and also submitted it, so it should be available in the 6.x repos soon enough assuming I haven't made any errors. So you could just wait for it to be in the repo, or like I said, pm me and I'll send you the new package for irssi