Well, there's been a lot of talk on these boards recently about Homeworld/Homeworld 2, so out of nostalgia and disbelief that Homeworld 2 supposedly doesn't work on Vista, I decided to reinstall it. Of course, the patched version didn't work and all the mods need it, so that wasn't fun.
After a bit of digging around the 'net, I figured out how to make HW2 run with no problems on Vista/Vista 64.
The reason it doesn't work isn't some compatibility thing, it's Vista's own DEP (Data Execution Prevention) halting the executable from running. DEP is designed as a security measure to stop programs from accessing certain things and in certain ways, so there must be something in HW2 that it doesn't like. Unfortunately, it's not possible to add HW2 to the DEP exceptions list (I tried, it says DEP is required to be on for the executable), so the solution is to turn off DEP entirely:
1. Click Start
2. Click All Programs
3. Click Accessories
4. Right Click on Command Prompt
5. Left click on Run as Administrator
6. Click the Allow button if it asks you for permission
7. Type or copy and paste this into the command prompt window:
bcdedit.exe /set {current} nx AlwaysOff
8. Hit enter and you should see the confirmation: Operation Completed Successfully
9. Reboot and DEP should be off.
After you do this (do be sure to reboot), you'll find that HW2 runs pretty flawlessly.
Of course, at some point you'll probably want to turn DEP back on, so:
bcdedit.exe /set {current} nx optin
Now, it's pretty hard to mess up your PC if you follow this exactly, but I'm not responsible if you do 
This isn't a "known fix to get HW2 working", it's just a way to disable DEP and it worked for my installation of HW2 and in theory should work for everyone.
