Multiple reports

I have a form frmPO with a subform sfrPO. On the subform is a combo box
cboProjNo from which the user chooses a project number. The PO could be for
many products for many projects. Once the user has entered all the products
to be purchased, there is a button to click to print the PO report rptPO.
There is also another report rptProjMat which lists material by project
number. When the PO is printed, I would also like to print the project
material report for each project chosen in cboProjNo on the subform. Not a
problem if there is just one project, but how do I write the code to print a
seperate project material report for multiple projects?

Ivor