I use two matched, calibrated 21" Hitachi CRT's, but only on my workstation, which has PrPro only and no PrE. My PrE copy is only on my 17" laptop, so I cannot comment directly on how it can best be utilized on a dual-monitor setup.
With PrPro (and PS, AI, InDesign, Painter, Encore, etc.), I have my main monitor (left) set up with main editing items (Timeline with a few Panels in PrPro), and the majority of my other Panels/Palettes are on my right monitor. Even with all that real estate, I have a dozen custom Workspaces for certain tasks. My normal is left monitor = Timeline, then Effects, Info, History docked together, and Audio Mixer, Source Monitor and Effects Control Panel docked together. Everything else, including my Program Monitor, Project Panel and Titler are free floating and on my right monitor. I have them tiled, so I can easily click on an exposed edge of the Panel to give it focus quickly.
Some PrPro users like to have the Timeline spanning both monitors, but even with mine butted to each other, the bezels on the CRT's breaks up my Timeline view, so I do not use that layout. With newer, small bezel LCD's, it might not be quite so visually disturbing, but I cannot stand to have my Timeline visually broken up.
There were some limitations in PrE, regarding what can be separated and dragged to a second monitor. I do not recall exactly what those limitations were, or if they still exist. I've just never used PrE on a dual-monitor system. Others can help you there.
Good luck, and when you get used to dual-monitors, and get your Workspace set up, you will NEVER go back. Working on my single 17" laptop display has taught me real estate management. Since I have had dual-monitors from the time that they became possible in Windows, I had forgotten how things used to be.
I agree with Hunt.
For video editing, two monitors are indispensible. I've got my workspace spread out, with lots of room for the timeline to expand as I add tracks.
I also often have one program running on one monitor and another on the other, as when I'm editing photos on Photoshop on my left that I plan to use in Premiere Elements or InDesign, on my right monitor.
Or I have my mail program full-screen in one monitor and my internet browser in the other.
As I say , once you get used to it, all this switching windows in a single monitor seems so clumsy!