Hello Manfred_Man, I'm pleased to hear that you found this forum and had a go at getting LB2 running again.
It's good that you narrowed your issue down to being a graphics-related one. I don't know why your game is being displayed in a small window. Are you using the dgVoodoo glide wrapper? If so, make sure that you have Fullscreen enabled in the settings.
If you have done that, but still have the problem, I suggest using the newer nGlide glide wrapper. Perhaps the older dgVoodoo that you are currently using doesn't like your graphics card/drivers for some reason. nGlide can be found at the link below...www.zeus-software.com/downloads/nglide
Also note that nGlide has very few customizable options, so may be less intimidating at first if you're not experienced with configuring glide wrappers.