Not sure about which window you are talking about, so to be on a safe side...

My monitor runs at 1280x1024.
I set up Win98 inside VBox to run at 1024x768, and VBox is windowed on my desktop.

When I run LB2, it switches to 640x480, and consequently, VBox window gets smaller. Therefore, I get a small window on my real desktop.

Almost the same thing happens when I switch VBox to "full screen". Only diff is that it fills the surrounding area of my (real) 1280x1024 with black border. Win98 @1024x768 and LB2 @640x480 are still at their resolutions and sizes, not over my real full screen.

When I choose "scale mode" I can resize the VBox window and maximaze it over my full (real) 1280x1024. However, then I get huge stuttering.
EDIT: This mode also crashes my VPC frequently when trying to switch back to another mode.


To sum up:
Not the best solution, but good enough. And very interesting for those that like to experiment with VPC.
But, in my opinion, the best solution - if you cannot run it on your OS - is to get another PC. Any old box. You can find those very cheaply, even in trash, or maybe you already have one.