I tend to go old school "frmMain"
nmaillet is correct you can develop "Mono" applications on a Mac using Monodevelop, I recently installed it on my iMac without issue. I also develop on windows using Visual Studio. I prefer Visual Studio as it has intellisense and good addins (#reSharper 7.1) that help greatly. But if you are just looking to learn C# development go with MonoDevelop, it'll get you started wihtout costing you anything or requiring new hardware.
welcome and Srećan Rodjendan! (Hope that's correct)
I own an iPad and an iPhone, but as a developer I oppose Apples edict that I can only develop using thier tools. Not even Apples "evil" competitor Microsoft forces me to use thier tools, I do by choice not by edict...