I did get the customregisters.i to work, I've switched to Asm-Pro as the debugger doesn't crash the machine unlike DevPac and Asm-One..
With the help of your code I managed to get a sprite to display on the screen, however I couldn't quite get my head around the bitplane stuff so I had a heap of random shit behind it!
What I did was filled #8000 of memory (at $21000) with FF's and pointed the start of that area to BPL1PTH with a move.l, I'm not sure why it didn't work as expected. The results were basically the same as not having any bitplane pointer defined except that it was a static picture.
I've uploaded the code to the zone in case anyone feels like taking a look at it for me.
Cheers