Hi 
Post it anyway, then add to it later.
I really like Stuart's neat trick of marking it as "NeedInfo" yourself so
that the QA Team don't spend any time on it until after you are ready to
change that status.
QA has a lot to do so chances are that they probably wouldn't get around to
your bug-report anyway but marking it in that way should make sure of
that.
Also if it's marked as "NeedInfo" and some other user stumbles across it
then they might be able to add useful comments too.
Bug reports do not have to be perfect. They work much the same way as
email threads in that you can add extra comments and attachments later.
Think more like conversation (maybe a little one-sided to start with!) than
report.
Regards from
Tom 