"slow" is relative.
"slow" at playing Crysis, mebbe.
Fact is you simply can't beat older, quality, hardware.
Your Dual P3/850 Supermicro will be faster and more importantly vastly more stable at many, many, many tasks than the latest top of the range core 2 quad laptop.
You don't have to know Mach3 that well (I don't, as a relative newbie to it) because Mach3 is code, and this applies to all code.
Still, this never has and never will stopped people from deliberately going out and buying something because they want it (eg core 2 quad laptop) and then whining because it runs some bit of code less than optimally, like it is somehow everyone else's fault but theirs.
Not only is stuff like your old quality hardware more suitable, it is also more affordable, than any new consumer grade kit, and when you ask me what computer is running Mach3 etc in my workshop I am as likely to answer "an ex corporate server I got for 50 quid, including the TFT" as I am to give you a precise Dell make and model number, because the fact is you can't claim to not be able to afford an older computer for the workshop, if you can't afford that then you can't afford Mach3, a bunch of machine tools, and light and heat.
cheers