What's a reasonable version of Windows to support for a new .Net application?

Question

If I develop a .Net application that's going to run on WinXP and Vista, as well as on a modern Mac or Linux under Mono, what are older versions of Windows where I will have to start thinking carefully if I want to support them? Does Windows 2000 for example run .Net and is it capable of any version of the runtime? Usually, older systems mean older hardware too, which might also be a problem, I guess.

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Edit: reading Joe's answer made me rephrase my question in the title. If Win 2k already has a lower common denominator with XP than Linux, that pretty much settles it for me. However, I'm still open to more info and will upvote additional helpful facts.

Answer 1

Version 2.0 of the framework is the last one supported on Win2k. We're also less than 18 months from the end of support for Win2k.

Do you want to support win2k, or do you NEED to support it?

Answer 2

Please be aware, that .NET 3.5 is not supported on Windows 2000. See the readme.

Answer 3

Since Mono runs on all your target platforms (Win 2000+, Linux and Mac OSX) you can develop your app with that instead of Microsoft .NET. Doing that will also reduce the pain of getting your app running on non-Windows platforms later (since as long as you don't use any platform-specific libraries it should Just Work).

Having said that, if you are going to develop something that can be compiled under Mono it's worth understanding its limitations.

For example, they have C# 2.0 fully implemented, but only partial support for C# 3.0.

Mono is also not .NET for Linux, it's an implementation of the CLR that is cross platform -- some libraries may not be implemented (although the core ones are).

Check out the wikipedia page and their home page.