I'm not sure what you mean by breaking up. Are you using VS2.75 or VS3? There is a very helpful FAQ for VS2.75. Use the menu bars to the left of the screen to navigate your way around. Does your system meet with the minimum requirements?
2)How do I combine sounds using the mixer function?
You may find answers at the VS2.75 User Forum or at the VS3 User Forum. You can post your questions there and usually have them answered by the people who use VSampler, and for the really tricky questions, by the guys who write and market the software, Maz, Thom and Renee.
The ability to save loaded instruments on particular channels so that you don't have to go through the lengthy procedure of re-loading every time you open an existing project or commence a new project. The demo version has the save function disabled.