I have done a couple thing since, but this did seem to help yesterday before I made several other changes.  

Execute Mach 3 with High Priorty instead of Normal Priority under Windows XP.  

With Mach 3 running:
You can open the task manager right click Mach 3 and select go to process.  Then right click the process and select prioty then high.  I was cautioned against selecting real time as it may take over the system resources to the point it may be slow or even fail to accept input from devices like the keyboard.  

To load Mach 3 with High Priority Automatically:
Right click the shortcut you use to Mach 3 and select properties.  In the Target field insert "cmd.exe /c start /high " infront of the rest of what you already have in that field.  

Now I plan to run Mach this way for a while to see how it performs, but I also just did a successful downgrade from SP3 to SP2 which I was told ran Mach 3 better with fewer problems.  I actually had an old copy of SP1 that I no longer have installed on any working computers.  Then I downloaded SP2 and upgraded, so don't go asking me about any magic tricks for downgrading.  I'ld have to Google it just like you would.  

If I still can't run 80K lines of code without a major walkabout in the wrong direction I'll be putting a non-integrated video card in next. 

Forgive me Bob, I saw you were having some trouble with the G540 (I can't remember where I saw your post) but did you try disabling ACPI in the Bios, and select "EPP" for the parallel port in the Bios of the PC?

Dave

I do have the LPT port set as EPP.  Not sure what ACPI is, but I will look. 

Bob, here's some very helpful reading as it helped me a LOT.

http://www.machsupport.com/downloads/XP_Optimization.txt

Dave