[TYPO3] Can't access backend admin or frontend website

[Matt Stanley]

I think I've successfully completed the 1-2-3 web-based install, but when I 
click the link to "Backend admin in new window" or "Frontend website in new 
window" I get the following error:

Database Error

The current username, password or host was not accepted when the connection 
to the database was attempted to be established!

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What am I doing wrong? Why won't this WORK?!?

Matt