Correct me if I"m wrong but when I was in an Apple store the rep told me the 15" pbook could have two web pages open side by side. I don't see how this is possible, my current resolution is at 1152x768.
Of course you can. You can have four web pages side by side on a 12" Powerbook for that matter. The windows will be quite small though.
To be a bit more serious. To have two browser windows side by side you'll need at least a 1600 pixels wide display in my opinion. Most web pages are designed for a minimum resolution of 800x600.