Specs:
Intel 2500k processor
16G RAM
GTX580 video
WinDOS 7 x64 SP1

Installed DKII from GOG.
Installed GOG's (or shall we say: timeslip's patch?).

Still had crashes on ALT+TAB.
I managed to resolve this by replacing QMIXER.DLL from the unofficial 1.8 patch.
While at it, I replaced the maps, too (the 1.8 patch makes a few changes).

Now it seems to be crash-free, however timeslip's patch ignores the resolution set in the registry and forces a less desirable low resolution.

That's it.
Here's some extra info/pointers for anyone who wants to experiment.

The GOG release uses Razor1911's crack (they just zeroed some strings out to make it look more official).

The GOG patch 1.0.1.30 adds DKII-DX.exe, PATCH.DLL to the game directory and updates the desktop shortcut to point to DKII-DX.exe rather than DKII.exe
DKII-DX.exe is the same as DKII.exe (Razor1911's crack), but it is "set" to load PATCH.DLL instead of DDRAW.DLL.

The unofficial 1.8 patch contains an EXE unwrapped with r!sc's safedisk cleaner, which is functionally identical to Razor1911's crack.

The unofficial 1.8 patch can be extracted anywhere as it won't verify the existing files.
Extract it anywhere but the DK2 directory. Then, you can copy over the QMIXER.DLL and the contents of Data\Editor manually to the same place in your DK2 directory, overwriting the files, giving you a 1.8-ish experience.

Well, that's all folks!

Thanks! I followed the directions here and was able to extract the 1.8 patch data successfully (last time I tried, the first map refused to trigger completion). GOG's QMIXER.DLL worked better than the 1.8 one for me, but it's an option for those who are having problems.

I did not say because I did not do it; I use the binaries patched by GOG/timeslip.
But,basically, yes, you can do it by hacking the executable. There's a string PATCH.DLL (just like that, uppercase letters) that you need to replace with DDRAW.DLL.
But, I am fairly confident you can achieve the same thing by renaming the file instead from DDRAW.DLL to PATCH.DLL, which is far easier than hex-editing.
Good luck!

hmm, by just copying the 1.8 over you don't use the patch.dll by timeslip.
And without the patch.dll DKII is not running at all on my system (ATI card, XP), therefore I patched the "patch.dll" string into the 1.8, as described on the keeperklan forum.

Additionally and independent, I patched the bytes for infinite zoom in... funny feature. Supreme-keeper called on the keeperklan forum ;)

It seems I was not clear. You copy GOG's DDRAW.DLL to PATCH.DLL and then use the 1.8 exe.

As for the super-zoom. Do no zoom out too much or else it will crash.