[SOLVED] - Upgrading Computer - Questions Regarding Compiling Older Code

32-bit programs run just fine on 64-bit Windows 7, because it has a compatibility layer built in.

I don't specifically remember whether or not VS 2005 runs on Windows 7, but there are Express versions of VS 2008 and 2010 available too - and they're free.

You shouldn't have any problems. When you compile a windows program, you specify the lowest version of Windows you support. This defines the maximum feature level that the Windows headers provides to you. So if you specify that your minimum is XP SP2, you won't have any features available that came in on Vista or Win7 (like task dialogs or jump lists). See this for details. Since you're making a game, you're probably not using very much Win32 functionality anyway so you shouldn't need to worry about anything.

Direct3D9 works fine on Win7 64-bit the same way it works in XP. So that's not a problem either.

In general almost all software that works on XP will work just fine on 7 (and Vista). There shouldn't be any need to select any kind of backwards compatibility mode - well written programs will just work, and most popular software that didn't work should have been updated by now.

There are things a programmer can do to make their program not work well on newer operating systems. For example hard coding the location or name of the "Program Files" directory, but those programs will usually not work as they should on some configurations of XP either. A good test for 7/Vista compatibility is to try running your program under a limited user account on XP.

One significant incompatibility you may see is with device drivers. There aren't any 64-bit drivers for some older hardware, which may mean you'll need a new printer for example.

Thank you all for your helpful responses.