Thanks for that, your advice and reading the vasm manual helped, but also I needed a kick up the arse to understand what linking actually was and how XREF and XDEF relate - I am an absolute beginner at this stuff. So now I can assemble stuff in vasm and/or devpac and link it all together with blink or vlink. Calling functions from modules such as the ptplayer work fine, I just need to understand how to get the player to do what I want without corrupting stuff on screen, I presume I am calling the functions with the wrong parameters. I'm not entirely sure what "AutoVecBase" refers to for example.
Perhaps this will be revealed in the HW Ref manual or some other dev tome, yet nothing is returned from the Amiga Dev Docs search on amigadev.elowar.com, so I wonder if this is some colloquialism I'm not privvy to.
Thanks again for the nudge in the right direction, though.