Thanks for all the responses guys. I went to my local fastener store this morning, who usually has EVERY type of fastener known to man. They only had straight shank 28 degree galv. nails - I picked up a box since I wasn't leaving empty handed and I had to run off to work. We could do screws since it's not a big area, but I'm thinking the nails will do.
I think we'll put down glue under the plywood, can't decide on what we'll do for fasteners yet. Ring shanks are hard to fine around here, and I'm taking time off to do this next week, so it's gotta get done then.. :P
Dan - I had a similar experience, trying to take a nailer 2x4 out of my shed when I put in a window. Just two nails, one on either end, it was ridiculous how tenacious it was.