Hi,
One of the ways of calling impromptu report from another report is the drill through option in Impromptu.
Select a column in the first impromptu
Go to Reports ->Drill Through -> Properties
All the columns of the Report will be visible select a column and then click on the Add Button.U can browse and select the report u want to call..provided both the reports have the same column on which u r trying to add the report.
To access the second report u can double click on the coulmn(of the first report) on which u have added the second report. This will take u to the second report.
Hope this helps,
Sandeep