I got a PC104plus DAQ card but don't know how to use A/D and D/A by using QB45, please guide me. Thanks.

I wouldn't know how to do this directly or through QB45 but you would have to learn some Assembly calls and call a series of INTERRUPTs through QB to interact with your DAQ card.

Did it come with a manual or guide to programming it?

It came with a library file but for windows.

Are there any manuals that come with it?

Since QB45 is dos, you probably need to ask the vendor for dos drivers.