As for forwarding all incoming e-mail at one g-mail account to another g-mail account -- it works fine -- I just tested it...
If you are looking at all current mail in one Gmail account to another you might try using the pop access and sync it with an e-mail client (i.e. outlook, netscape, etc.) make sure the e-mail file in the client is in mbox format (.pst will have to be converted) then import it to Gmail using several tools you can find simply by googling "transfer mail to Gmail" or wording to that affect...
Hope this helps -- I was able to transfer two years of outlook e-mail by converting to mbox format and importing with a tool from
Mark Lyons Page -- of course I did this sometime back...