We run a Navnet Vx2 system on our 4788 Bayliner. Currently we have two displays.

I would like to add a third display but was thinking about using my Dell industrial laptop and running maxsea software.

The challenge I have is that my laptop like most new laptops is running windows 7. It does have a windows XP virtual machine running, for use with older programs.

Will the maxsea software work in a XP virtual machine?
I am sorry, regardless if you are running MaxSea Classic (12.6.4) or MaxSea TZ; emulations (like VM) are not supported. This also includes trying to run these programs on an Apple using any emulations/VM. Apple can run MaxSea using BOOTCAMP (duel boot type system) where they are running a full version of the required operating system. What version of MaxSea are you considering running with your PC and the Vx2 system? Maybe we can find a way to accomplish your goal.
I wasn't sure what version of Maxsea. I was going to purchase it.

I may just add another Navnet display instead. This would give us three displays total. That way we could dedicate one display for radar, sounder, plotter.

I am not a big fan of the split screen mode. Nothing wrong with it per se, it just makes each display 1/2 size.
For plotting functions and sharing NMEA data from the Vx2 network, I would suggest Maxsea TZ Navigator which can run in XP Pro, Vista, and Windows 7. (both 32- or 64 bit) If you are seeking to also control the radar and sounder with the PC, then you really have only one option. That would be MaxSea Classic 12.6.4 NavNet Explorer, but you MUST run it with XP Pro. Your plan of another station display sounds like a good option. If you need any help with setup once you get it, feel free to give us a call in tech support.