I read:
I have an old Pentium 1 MMX 100 MHz laptop that I would like to use for MIDI controlling with Pure Data under Linux. Is it possible ? I'm afraid the Tcl/Tk GUI will be very slow
I ran pd (debian, blackbox) on a 120Mhz pentium a while ago even doing audio (with -r 22050) but with -nosound only for midi it should be fine.
Also, which Linux distribution would you install ?
I would always go for debian, in your case maybe slackware is a better choice.
just make sure you kill everything you don't need, (down to syslog if necessary) make a custom kernel with preemption turned on and turn off swapping if you have enough ram.
good luck,
x