lectricpharaoh

It also depends on what programming language you're using, and whether you're writing native code or not. If you're writing native Win32 code in, say, C++, then you need to be careful which API functions you call. If you're using one of the .NET languages like Visual Basic or C#, you're unlikely to run afoul of portability issues unless a) the machines in question have different framework versions (targeting v2.0 seems a safe bet these days, and v3.0 is becoming more common) or b) you are calling into native code via p/invoke (in which case the native code functions must be supported on your target OS).

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