I personally go silly with killing whatever I can on my PC. My motto is if it's not needed then kill it.
Regarding XP SP2 someone once swore that he had tested SP1, 2, & 3 and 2 was the ONLY one that didn't give some random issue. Now I believe his system was one of the older Candcnc plasma systems (MP3000-DTHC) which have a plugin written for Mach3, so whether the issues were related to the plugin or Mach3 itself I have no idea.
You need to install XP in "Standard PC" mode. This is detailed in the "XP Optimisation" guide which I believe is available from the Mach site. Search for "optimization" on this site or even Google Mach3 XP optimisation and you might come across it. It's normally a .txt file.
I disable anything in the bios that I think is not needed.
No other programs running or installed, the PC is a machine controller. I uninstall any XP programs like Internet Explorer, etc. My ethernet is disabled.
I even go into "services.msc" and turn off & disable a whole bunch of things that are just XP crap and are not needed. Google about disabling XP services and use your own judgement about what you think you can turn off. I'm no expert so don't want to recommend things in that area.
I hear all sorts of stories about how Mach can be happily chugging away for hours / days then capow it suddenly goes wonky and smashes a tool. Was that some service running in the background that caused it, no idea, but the less things there are running the less chance of one interrupting the program flow.
This is what I personally do and no-one has recommended I do this, it's just a calculated guess I made that maybe this will make Mach3 more stable.
I've occasionally found a PC that just doesn't work with Mach3, no matter what I do. I seem to have had best luck with Intel motherboards and quite a few of those have gave me a good driver test right up to 100Khz.
Keith.