At least when I tried to play some older games with VMWare, I think normally the games would be in a small "window", unless I set my Windows desktop (the real one, not the XP running inside the virtual machine) also to some low resolution first.
I think those virtual machine applications are not really designed for retro-gaming in mind, so they don't care about such gaming-specific things like the ability to run an application on a lower resolution in full screen (zoomed). I didn't find the virtual machine apps (I've tried VMWare and VirtualBox) that good for retro-gaming.
Ultra_DTA: So when you guys play older games, from GoG or otherwise, how do you guys play them? Do you guys use older monitors, or do you simply tinker with the resolutions? Do you try to get it just right, or do you just play them when you get something that works?
GOG games are designed to run on modern Windows versions and modern PCs (that's the whole business idea for GOG selling those old classics, ie. so that you wouldn't have to tinker with them), so there is no need to try to run them on virtual machines. What Windows version are you using, and what kind of computer? Most GOG games should probably run fine on it as is.
For non-GOG games, or a few GOG games that do have issues on the latest Windows versions or modern graphics cards or the CPU speed (e.g. Interstate '76, Alone In The Dark The New Nightmare etc.), I might play them on some older PC I have, possibly running Windows XP. Quite often the problem is not necessarily the Windows version, but e.g. the graphics drivers.
I tried virtual machines before (mainly VMWare), but I feel they are not really that good solution for trying to get old games running, even if sometimes it might work passably (mostly not, in my experience). Maybe Wine running in Linux is a better solution for the problematic games?