Are normal PCI cards compatible with the PCI Express Slot?

I am looking into building a new computer, but not too sure about PCI Express

Mainly, I will use this computer to record music, which requires 2 PCI slots, one for the master card and 1 for the slave.

I like the SHUTTLE bare-bones systems, but they all only come with 1 PCI and 1 PCI Express slot

Will a normal PCI card work in a PCI Express slot? (theres happens to be the 16x PCI Express) assuming the mobo has on-board graphics capability

I see alot of threads of people trying to use PCI Express cards in normal PCI slots but not the other way around