If you want the slide shows to occupy the entire screen together, look at
PowerShow at
http://officeone.mvps.org/powershow/powershow.html.
Specifically, look at its TickerShow feature at
http://officeone.mvps.org/powershow/powershow_ticker_show.html.
If you don't mind window borders and menus surrounding the slide shows, do
the following:
1. Open both your presentations (say, ppt1 and ppt2) in PowerPoint.
2. Make ppt1 active and select "Slide Show" | "Set Up Show..." menu item.
3. Select "Browsed by an individual (window)" box and click OK button.
4. Start ppt1 slide show.
5. Make ppt2 active and select "Slide Show" | "Set Up Show..." menu item.
6. Select "Browsed by an individual (window)" box and click OK button.
7. Start ppt2 slide show.
8. Right-click on the menu at the top and select "Customize..." menu item.
9. Select "Commands" tab and select "Window and Help" category.
10. Select "Arrange All" command from the command list, drag it to the
"Window" menu and drop it.
11. Click "Close" button.
12. Select "Window" | "Arrange All" menu item to get both the slide shows
next to each other.
- Chirag
Shortcut Manager - Assign keyboard shortcuts to menu items and macros
http://officeone.mvps.org/ppsctmgr/ppsctmgr.html