You can't easily switch the account to another one, I am not sure anything less than a factory reset will do so. It's not a Streak thing, but common with android phones (especially up to 1.6 at the least).
Newer versions may give you the option to sync up from multiple accounts, but still have the one account as the main one binding the phone. So if you're ok with that, it may just be something to wait for. In the meantime you should be able to have your new account grab mail from your other account and forward it under your old address in mail.google.com under Settings and the two tabs "accounts and import" and "forwarding and pop/imap".
Before you do, grab and store a copy of your current mail, as the wrong settings whilst you're getting it setup could temporarily send things to the wrong place (or a black hole).
As a side note; Smoker - what did you use to grab that screenshot? I had been using ADB and the android SDK to take screenshots but it seemed very hit and miss whether it could read the screen display. Just wondering what you're using so I might give it a try if different. Thanks.