Very late reply, but I'm new to GoG and my interest in Stronghold was also just revived.
This appears to work for me, so far:
It's the same program as linked to in that YouTube video earlier in the thread, but this download checks out as clean with Malwarebytes and Avira and Comodo and WinPatrol also haven't caught it doing fishy things:
http://www.filefront.com/13838785/D3DWindower-English/ 1. Extract to your Stronghold Crusader folder.
2. Open D3DWindower, click the + sign and select "Stronghold Crusader.exe".
3. Click the "Settings..." button (right of the computer icon).
3a. Tick the 'Use Windowed Mode' box under the Common tab.
3b. Go to the Direct Input tab and tick the following: Use Direct Input, Cursor Clip, SetCursor Pos, GetCursor Pos.
(These settings mean you have to alt-tab to get out of the Stronghold window, but without them, the map will autoscroll and basically make it a major pain to play, if not downright impossible. Game pauses when you alt-tab, which can be both a good and a bad thing).
3c. Click OK.
4. Click the computer icon to start the game.
Caveats:
Only tested on Vista 32bit.
Tested with retail Stronghold Crusader v1.1 from the SH Warchest (for now. I suspect I'll end up getting the GoG version).
Only tested on the tutorial and the first mission of the first campaign so far.
Note:
There appear to be some minor graphics glitches, but I'm not really sure they haven't always been there and I've only seen them when moving a 'ghosted' building over the terrain before setting it down prior to building it. It's quite possible that fiddling with the settings may fix them, if they are due to D3DWindower.
I haven't tried D3DWindower with Stronghold, but it seems very likely it'll work.
Edit: Seems to work fine with the GOG version of Stronghold too.