My understanding is that little (if anything) has actually changed in the delivery of IWP from 11 - 12 - most notably IWP doesn't support themes…
The only way to know for sure is to try it - since you've already bought FMS 12, set it up, take a copy of your file, convert that to 12, put it on the server, and try it in IE 6, if that's successful (which I expect that it will be) then carry on and convert...
I haven't tested it, but in that document you will find the supported browsers listed.
Requirements for accessing FileMaker databases on the web
To work with a published FileMaker Pro database, web users need:
• access to the internet or an intranet.
• the Internet Protocol (IP) address or domain name of the computer that hosts your database file.
• These requirements may differ from those of the FileMaker product that hosts the database.
• Instant Web Publishing is not supported from iOS browsers on iPads, iPhones, or iPods.
• Instant Web Publishing is not supported from runtime solutions or Kiosk solutions because runtimes cannot be shared over a network.
Hope this helps.
Beatrice Beaubien, PhD
i2eye, Toronto, Canada
FileMaker Business Alliance
FileMaker 11 Certified Developer
Knowledge Translation Certified Professional