I have no idea what a Monza version is, but I do know what a Selespeed is.
The Selespeed transmission is a manual gearbox operated by a computer. With 'plus' and 'minus' button / paddles you can change gears, similar like an F1 driver. The old 156s (< 2002) have buttons on the steering wheel to operate the gearbox and the later versions (>= 2002) have paddles behind the steering wheel.
It would help if you posted details about the car you're looking at (or the website where the car is advertised) and your location. (Hint, fill in the location section in your profile.)
The latter is important because different geographic areas offer cars in different trim levels and with different options. For example, Aussies can buy a Monza badged 147GTA. I haven't heard of a 156 Monza version, but maybe it is a local specialty or a dealer offering. http://www.alfaowner.com/Forum/showt...ht=Monza+badge
Spec looks similar to a Sportpack/Veloce model ...
Like others have suggested, maybe a local/dealer variant.
The Monza 156 was definitely an Australian special edition including the side skirts, momo leather trim, carbon-fibre-look console, red-on-black dials, and green cloverleaf badges. I'm not sure about suspension changes.
We bought a 2000 Monza Selespeed a few months ago - here are some photos if it helps identification: