I'm not running these plug-ins any longer now that I run Pro Tools LE on a Mac OS, but when I did run the Kjaerhus Audio Classic Series plug-ins it was in Cubase SX on a Hewlett Packard Pavilion dv8000 lap top that had a 3.0 Ghz processor and 2 GB of RAM. I never had an issue running any of these plug-ins in the years that I used them. All of them always ran smoothly without performance problems, as none of them take up much processing power at all.
If you have a system that is compatible with the Kjaerhus Audio Classic Series plug-ins, there is definitely no excuse not to have them. While they aren't the best sounding plug-ins that I've heard, especially when compared to some of the newer ones, but considering that these are pretty old for plug-ins and are FREE, they sound pretty good. In fact, I'd stretch to say that they sound as good as any free VST plug-in that I've had or used. Go download the Classic Series plug-ins now if you haven't already!