Seems to me like you want to drop quite a bit into an old bike. If you start talking about drivetrains, brakes, shifters, etc., you're now talking about enough to cover an entry level brand new road bike.

Take for instance the Specialized Sirrus, which ranges around $500 for a 2005 (and I've seen 2004's for as low as $400)... In other words you might do better saving your pennies and making a move all at once than upgrading an older bike. More bang for your buck in the long run.