So, in conclusion, here's the full guide for those who don't have the issue fixed yet:
This is how to fix the Unreal II intro problem that appears in Vista and Windows 7:
1. Download the Windows 2003 DirectMusic fix from here or here.
2. Extract it and open the folder named "system32" in it. Note their names, then go to C:\Windows\Sytem32 (32-bit systems) or C:\Windows\SysWOW64 (64-bit systems). Find matching DLLs and back them up.
3. Create a System Restore point just in case.
4. Replace the corresponding DLLs in C:\Windows\Sytem32 (32-bit systems) or C:\Windows\SysWOW64 (64-bit systems) with those that you found in the downloaded archive by using Replacer or doing it manually.
5. Restart the system and check if the problem is gone.
6. If not, open the Registry Keys folder in the archive and apply them all (32-bit systems only). Note: Needs testing if this is required or not.
7. Restart again and the problem should be fixed.
The problem itself was caused by Microsoft bundling a srtipped-down version of DirectMusic with Windows Vista and up which doesn't support all of the DirectMusic Script commands, thus breaking the Unreal II intro and probably more games.
This is how to fix the Unreal II intro problem that appears in Vista and Windows 7:
1. Download the Windows 2003 DirectMusic fix from here or here.
2. Extract it and open the folder named "system32" in it. Note their names, then go to C:\Windows\Sytem32 (32-bit systems) or C:\Windows\SysWOW64 (64-bit systems). Find matching DLLs and back them up.
3. Create a System Restore point just in case.
4. Replace the corresponding DLLs in C:\Windows\Sytem32 (32-bit systems) or C:\Windows\SysWOW64 (64-bit systems) with those that you found in the downloaded archive by using Replacer or doing it manually.
5. Restart the system and check if the problem is gone.
6. If not, open the Registry Keys folder in the archive and apply them all (32-bit systems only). Note: Needs testing if this is required or not.
7. Restart again and the problem should be fixed.
The problem itself was caused by Microsoft bundling a srtipped-down version of DirectMusic with Windows Vista and up which doesn't support all of the DirectMusic Script commands, thus breaking the Unreal II intro and probably more games.