thanks for all your suggestions
I will try to install a minimal Linux (like slackware or knoppix or something like this), with the most simple window manager I hope it will work
Currently, with W98, it's quite difficult to use less than 100% CPU Maybe W2k or Linux would be better This is an old laptop that was to be thrown when I got it for free ; I used it for playing MIDI sequences from Cakewalk into a hardware sampler
I will also use this PC for non realtime audio processing and composing (with Scilab software)