I am absolutely OPPOSED to a java chat built into every page... I absolutely DESPISE pages with embedded java apps. I would absolutely stop coming here if that was put in place.. it takes a good 30 seconds to load java on each page, during which time your browser is frozen and it slows your computer to a crawl. then it would have to log you in each time you visited a page, it would log you out each time you clicked a different page, and it would be a huge clutter wherever it was put.
As for the choice between an onsite chat or a java irc client, I'd go for the irc idea... This site is fairly popular, but I think it would stagnate if it were restricted to people who happen to be browsing the site at the moment... at least with irc, you can use your own client, you can be on it without being on the site, and it may draw people from other laser forums, or just general laser enthusiasts who happen to be on irc at the time. Also, I'm guessing a site-specific chat would be a liability, since it's hosted exclusively by the site, LPF would be responsible for moderating it, whereas if it were hosted offsite on some random irc server, LPF wouldn't be liable for its content.
Two good java irc clients that come to mind are JPilot and PJIRC.
That said, I don't really see the point. The forum allows PM's, and allows you to put MSN/AIM/ICQ links in your profile... I'm thinking a link somewhere to laserchat.org would be more than enough.