We're approaching a point of replacing several of our developer PCs and would like to move up to 64-bit to maximize the hardware/life of the PCs but we also need to support several legacy VB6 applications. That said, Microsoft says it's not supported, but that doesn't necessarily mean it doesn't work. However, support's not important on a dead tool so long as it's functional.
Not sure about 64 bit, but I recently had to install the VB 6 IDE on Windows 7 (32 bit) and couldn't get the installer to run. I ended up using Windows XP Compatibility Mode (essentially a virtual pc) and was able to install and use VB 6 on the virtual image. It was a bit of a pain to configure, but once I got it working it ran fine.
I'm told that 64 bit is not a problem but it doesn't like Windows Vista and up.
If you really need it on 64 bit Windows Server 2003 x64 should work.
Folks on the VB6 newsgroup report they have managed to get it working on Windows 7 64 bit.
There's this step-by-step guide on how to install the IDE on Windows 7 (including 64 bit).
If that doesn't work (scrapes barrel) try this old tip about persuading the install not to install the Java VM?
Or (scrapes hole in barrel) these tips from an article about getting the IDE working on Vista?
I tried it, but it didn't work. It was a while ago, so I don't recall exactly what the problem was. Why deal with the hassle of trying to make it work when Microsoft provides Windows XP Mode for free?
Speaking from experience (I run VB6 almost every day in Windows 7 - 64 bit), there is no problem getting it running, in fact you do not have to run it in any kind of compatability mode. There are a couple of Caveats though: