New User - Questions regarding PzC

[jckerr4]

I am interested in playing PzC, and I am curious regarding which game to puchase from HPS.
I have been playing SSG's Battlefront and Kharkov, in which I have had some sucess, and enjoyed.
Someone recommended HPS, but I am not sure which game to order.
My intention would be to purchase, spend some time playing the AI until I can stand on my own 2 feet, and then start some PBEM.
My Questions are:
Which PzC is best to start with?
Will it work with Vista?
Will I be able to find opponents on this site?