Computers confound me

I'm printing out envelopes from within Pages.app. When kicked off from my Macbook Pro, they print out fine. But the same document prints totally wrong when printed from my Mac Pro. On the screen, the document looks the same. The printer behaves properly for other documents. If I try to fix the problem by changing the orientation in Page Setup, the envelope document looks totally wrong (becomes vertical instead of horizontal -- clearly not the desired result). Argh.