KT7A, Mobile Athlon XP 3000, and yes most sites fall down and go boom these days if even one of their 9000000 content displaying or tracking scripts fails.
Edit: Why does this site insist on munging perfectly good small PNG files?
In general it seems PHPBB with an older/more compatible theme is fairly friendly to older browsers. Another good example is good old Mozillazine: http://forums.mozillazine.org/ - it looks and feels like a proper forum should.
I really, really, wish Winworld had not had to move away from PHPBB, but I have been told that underneath the hood PHPBB is a mess.