Sweet, got it working in one pass :) Thanks guys!

If I've got these layers to splat

base
tex1 + alphamap
tex2 + alphamap

then I'll need 5 textures.

I was looking at graphics card specs, and the GF3 supports 8 texture blend ops and 4 textures per pass...does this mean I can't use the FFP in a single pass, but I can use a pixel shader in a single pass if I use the RGB channels of a single alphamap for the separate textures?

I'm using a Radeon 8500 card, and even though it supports pixel shaders, enabling PS support is always a great way to slow any game to a crawl. Hitman 2's systems relied on pixel shaders. As a result, I was unable to play it and returned the sucker the next day. I guess it won't be a big deal in about two or three years. But until then, I see it as dangerous to use any PS system that the user cannot freely turn off and on.

Making your system use 4X more video memory in older cards doesn't sound like a good idea to me. You should at least find a better alternative, or shrink the textures down to 1/4 of their size.