Which version of ASP.net

[shady]

I'm about to embark on learrning ASP.net. I'm reasonably proficient in ASP, and realise it's a different kettle of fish, and not sure which version I should start with. I have IIs 7, which supports 3.5, but the server i'll be developing for is Win2003 (at the moment) Is it practical to jump into 3.5, ie, will applications run on win2003/iis6

Thanks