You could try having your main one at 1280x600 (if your comfortable running at that resolution) and your other one running at the same, but overlapping part of your main and just have it in the background?

-edit

Looking at the screenshots of that setup (with one always ontop) you could get it to work like that, change the font size in chat to 18pt (still hard to read, but better .. or get a chat mod like Prat2.0 to change it so its bigger) and then just get ZQB to make it so its easier for you to accept quests/hand in quests/etc.
Because you can easily see NPC's on the small one, and if you use ZQB then you just open up npc chat on both and the slave copies quest handins/etc that the main does.