Just to share my experience with really old hardware.
I found a couple of IBM Network Station in the dust bin of a friend company and took them home. They have a Pentium 166, 128 mb ram. I fed one of these with a Nexus and an avermedia 771 (DVB-T). I installed a Suse 10 kernel and using the drivers included in the distribution (installed latest firmware) VDR compiles and Nexus is perfectly recognized - I'm working on the aver, recognized by the kernel but not working on VDR.
I want to say that VDR seems to work flawlessy in this slow environment.
Recording of one channel (RAI 2 on hotbird) results in a 40% CPU, of which 20% for VDR and 20% for system. Ram is almost fully used. Recording of two channels (RAI 1 and RAI 2) makes VDR really irresponsive, but the recordings seems to be ok.
Francesco