Lois,
Did this problem start around Dec. 18th or a little later?
Have you tried with IE7, or just Firefox? IE7 would use the ActiveX verion of the uploader and other applets vs. Java Runtime Environment with Firefox. That would be a good test.
I have tested with Firefox 3.0.5 (latest) and Java Version 6 Update 11 (build 1.6.0_11-b03 also latest). I'm running WinXP-SP3 at current service, and haven't had any of the recently reported problems with the one-page or the image uploader.
I am aware that Microsoft rolled a IE (all version) update around December 18th, and it does have different install criteria for different versions and service pack levels of Windows (even a security fix for IE8 Beta). That date does seem to mark a point where alot of strange problems started. It does seem consistent with those now reporting update to Service Pack 3 has fixed Win-XP issues.
For those investigating, the update is KB960714 and here is the Knowledgebase article:
http://support.microsoft.com/kb/960714Have you installed the latest Vista Service Pack?
Danno