When I mentioned to add the overflow to your CSS I meant your style sheet tag and not inside your source document. Maybe that's what's causing an issue in IE6.
The CGI Email in cPanel should be disabled on all the servers. It is not a secure solution.
Also, if you ask the help desk this is the response you will get.
My opinion is Firefox is rendering it as you have coded it and IE is rending it as you want it. This is a common occurance between browsers. While Firefox is standards compliant IE6 is not.
Do you have a link?
Since you have seen an increase of more than 30% membership you can use that figure to estimate how much more bandwidth you will need. If you expect even more growth factor that in as well.
That does seem unusally large. I checked all my accounts and they are no where near using that much space.
Check with the help desk, maybe they have an answer.