I think "downgrades" are becoming more popular these
days...(Vista to XP.....iMovie08 to iMovie06....etc.)
I doubt you can install FWCS3 with a FWCS4 serial, but you
can certainly call Adobe's customer support to find out if they
will send you one.
I think Adobe should consider posting a free download of
FSCS3 that will install with a valid FWCS4 serial number for users
to run until Adobe can fix the text engine in CS4...similar to what
Apple did with iMovie06.
Having the option to downgrade to CS3 for those who purchased
an useable CS4 seems only fair.
Is there an official policy yet? Weeks ago, I suggested many
of my co-workers get FW, which currently happens to be CS4, but now
reading all the bug reports, what can I do?