PCI Memory Space?

I have a card that uses a PCI to VME bridge. When the card comes up I can
get the register base for the card configuration, however in order to write
to VME space I need to have an unused block of PCI memory space that I can
program the card to use. How do I find empty block of PCI memory space to
claim for a piece of hardware, and tell QNX that memory belongs to that