Hopefully someone can find a solution for you, but I can tell you it's not universal on all systems. I have the game installed on my Win7 Pro 64 bit rig and it works fine. I've also installed a bunch of mods without issue. So it will definitely work. Looks like it's just a matter of figuring out what quirk of certain systems is causing the issue.
For reference, here's what I've done:
When installing my OS, I installed to a Solid State Drive. In order to cut down on writes/rewrites, I moved my User folder to a different hard drive altogether (this involved a registry edit, but it's a fairly simple process). I have my Games folder installed under Programs (not Programs x86), but it's also been moved to another drive and simlinked through Programs.
I installed BG2 like any other game into my Games folder, running as Admin. Once installed, I changed the properties of the desktop launcher to run in Windows XP SP3 compatibility mode and set it to run as Admin as well. (Even after doing that, I always right-click the launcher and choose to run as Admin when I play).
I then installed BGT with the Unfinished Business mod, BGTweaks for BG2, and the widescreen mod using GoJays' guide. Everything works great.