What I would do is set the 80 gig up as master and install a fresh copy of the OS on it. Then, with the 4.3 gig drive as slave, I'd make a directory and copy the contents of the drive in to that directory. (Go watch Baseball while waiting or something.) When done, remove the 4.3 gig drive from the computer and put it someplace safe. (I like to put it in the case of an another computer...and use it.)
After that, you'll have to install all your programs from scratch, but doing it this way is worth the hassle. You don't get migratory problems, and have a clean registry. You've also got your old drive's contents in a directory of its own so you can get your wall paper and stuff.
As for your screen being twice as big, I need more information to help. Right click on the desktop, go to properties, and look under the settings tab. What is the "screen size" slider set at? Also, what does it say the monitor/graphics card combo is? (Default monitor on Standard VGA adapter, for example...)