Why go through all of that effort?
According to our site stats, between Firefox and IE our combined traffic comes in at around 93% or rather 93 out of 100 users are browsing with FireFox or Internet Explorer. About 5% are using Opera & Netscape. Most people who use the internet regularily have multiple passwords and accounts for shopping, ebay selling, email, online banking, online service logins, credit cards, paypal accounts, and so on. That's exactly why most browsers these days support the ability of storing and reusing user names & passwords .... so that when a user goes back to the site (such as this forum)
where a login/password are required, the browser recognizes this immediately and enters the correct information automatically.
I actually don't know anyone who doesn't use those browser features ... that's specifically what those features have been designed for - to make logging in a lot easier and faster. So, even if you were to do what you suggested above, chances are that about ... 95% (or more) of your guests or members wouldn't even need or make use of such an option since every login after the 1st one would be almost instant ...
Just some thoughts to try and help save precious time!