.net 2.0 features will be missing from Vs2003 ( generics, partial classes, anonymous methods, etc).

Minor correction...in VS2005, anonymous methods are available in C# but not .NET

But in general, a good point - focusing on VS2003 means missing out on powerful and more recent features, such as .NET Generics. Given that features in the 2.0 and 3.0 framework utilize generics, 2005 is a better 'foundation' than 2003.