So the first suggestion that MPlayer makes for slow computers is to use the ALSA sound drivers. These drivers are included in later kernels, but not the 2.4.x series. Instead of taking the sensible course of action of downloading the source tarball and compiling them myself, I took what I thought would be the easy way out and started using the Debian pre-compiled kernel and ALSA modules. Except that mkinitrd wasn’t producing an init image and I had to make it by hand. Except that I now had to recompile the NVidia driver (ugh) and the linuxtv modules (argh).
Once I’d done all that however I could watch digital TV on the PC with no problems…until I actually wanted to do something on the computer that is. It’s then that I noticed that MPlayer wasn’t using the NVidia video output driver, that’s my next problem.