It's important that these GUIs be portable (we use both WinNT and Unix), and the GUIs themselves will have little function except as a pretty front-end for data entry and updates.

This looks like the sort of problem a webserver intermediate tier solves. This has loads of benefits - such as no need to roll out libraries of perl to all your users, ease of maintenance...(copy & past other benefits from your favourite 3 tier arch slideset) - and makes the whole thing just a question of a CGI-script (the CGI script coul dbe a java servlet or a perl script)

If you want to use Java then of course you can do so but from what I'm reading the GUI requirements are pretty minimal and these days people are instantly familar with browser based queries.

Dingus