I have to explain the situation I have.
I purchased a Mac Pro sometime back to use in my office but the person in the office next to me also frequently has use for a Mac Pro and since we can't purchase two Mac Pro's now we decided to set up a system with multiple monitors/keyboard/mouse. We ran a 2nd DVI Cable and a USB Hub over to the other office and use that for a second monitor hooked onto this Mac Pro plus a 2nd Keyboard and Mouse. Fortunately the distance was not too far and it worked out well.

The problem we're having is trying to figure out how to do the Screen Mirroring/Spanning. The Mac Pro has two video cards. Video card 1 is the Nvidea 8800 GT and the 2nd card is an ATI 2600 XT. I have the main monitor in my office which is a 22" Samsung Widescreen hooked up as video 1 on the Nvidea card. The 2nd monitor which is an Acer 19" Widescreen monitor has been hooked up to both video 2 on the NVidea card and even video 1 on the ATI.

We have selected to do screen mirroring and this was our original plan except once screen mirroring is turned on the graphics seem to run much slower on both monitors. When a window is moved it is kind of 'jerky' and everything seems slightly slower. Is this normal or can it be fixed?

We then tried simply spanning the monitors and fortunately that fixed the 'jerky' problem. In a sense it even allowed us to have our separate workspaces. I could have my workspace open on my monitor and hers open on her monitor. Of course even though we have two keyboards and two mice they can't be used at the same time.
-Is it possible to set up a system where we could use both mice and keyboards at the same time on separate monitors? The only way I can think of possibly doing this is through something like virtualization but even then I think even with separate monitors only one keyboard and mouse can be used, right? I know you can select for a program like VMWare to either use or not use certain USB devices but yet you can't run OS X in virtualization, can you?
-Also, another issue we ran into with this is screen sizes. It may be because of the smaller 19" monitor but it seems to want to make the screen resolution lower on the 22" monitor. I have changed it to a larger screensize manually after the computer does it but then the screen is not the full width of the 22" monitor.

Screen spanning definitely seems like the best solution to us with the separate workspaces and better speed than mirroring. The big problem we have with screen spanning though is that the 2nd monitor doesn't display the dock at the bottom or the pull down menus at the top of the screen. Is it possible to display them on both monitors?

Thank you for any help with the above questions.