oscam can easily be compiled for the N900 (I have already done that too).
But you may not need to do that. If you use TVheadend on the N900, than you can just point it to a oscam server on a remote desktop/server.
Since you have only 1 USB port you will want to use it for the dvb-t adapter, not a smartcard reader.
The problem is that Tvheadend does not compile for ARM using the old version of gcc used by scratchbox, you need an updated version.

The other problem is that the kernel used by the n900 does not contain drivers for de Picostick. On ubuntu I only got it to work by installing a new version of v4l that I patched for as102 support.

If you could give a how-to guide, on how I can compile the v4l modules for power kernel myself, that would be a lot more useful. I have already setup a the SDK, and I build my own power kernel package and installed it on my n900 successfully, that isn't the problem.
I don't know how to add a driver from on updated v4l to the kernel.
So if you could give me a step by step guide on how you compile your v4l modules for power kernel, I might be able to figure out the rest. (and will share any progress made, off course)