Hi MBL
A Support Specialist from SMF had a look around in the forum settings earlier today and couldn't find anything that was obviously wrong or that might have prevented you from being able to post multiple attachments.
He suggested increasing the size limits for attachments to see if that might make a difference. For the moment, they are set at 250kb per attachment. Please try once more to attach 3 or 4 pics to a post (nothing too large to begin with, just the size that you normally would be using).
If it still doesn't work, then I don't know what we can do. I think we'll have to assume that something in the SMF program is not compatible with the system you are using.
edit:I know you're not keen to change browsers, but Mozilla is a very good alternative to IE. It's free, it's just as easy to use and only takes a few minutes to download and set up. I installed the Windows version yesterday for the very first time, and I find I prefer it to IE already... I'm seriously considering making it my default browser after 5 years of using nothing but IE.
Mozilla 1.2.1 is the only version available for Mac OS 9. You can find a link to download it and the bottom of
this page if you're at all interested. Sorry I can't provide a more workable solution for you.