Tom,
If you go in the "Layouts" window, select the layout you want to put a condition on and then hit ALT+ENTER, this will bring up the properties window. In this, you have the "Action" item. Click on the "Layout will be printed", which brings up the Expression Editor.
You can then use a condition that reads something like:
IF([Amount] > 100, SKIP, PRINT)
Hope this helps,
Eric