I think what you will need is two computers, one for the music show and one for the on screen presentation. That is exactly how I do my shows.

PS: If you don't have a second just borrow a friend's laptop for the screen show, odds are it will already have Powerpoint installed, set your slide transition times and reveals hit play when you are ready to start the presentation and you are done, homefree. Unless I am missing something here this should be a pretty simple operation. I know sometime us creative types tend to over think a realtively simple production.

Later,