I was running a test piece from Vector Art 3D machining. It is the fleur d'li. The first roughing pass went fine. During the second pass, the stepper motors seemed to stall and buzz loudly for about 2 seconds and then the job continued without intervention but shifted about 2 inches right and down (Y-axis). The Z axis seemed to be fine.

I am running a Xylotex 3 axis system with 269 oz motors. The motor speed has been cut back to around 50 ipm and the acceleration is not agressive. I used less than 8 ft long shielded cables to the motors. The spindle is a Porter Cable 690 series. I have only been up and running for a few days now. I am not 100% everything is correct with this homebrew machine. From what limited cutting I have been doing, everything that has gone wrong so far has been operator error.

I am running a 750 mhz Dell Laptop under win 2k. It is a clean machine dedicated to running the Router. I am running a licensed version of Mach 3. I disconnected the wireless card and it has no other networking/firewall/ anti-virus software running. It is version 1.90.037 of Mach 3

I am thinking the laptop may be not enough horsepower to run the job.

Can anyone give any other suggestions?

Stepper motor stalling for sure. You either need; higher voltage, less 'stiction' or friction in your slides or ways, or turn the rapid speeds down some more. Doesen't sound like it's the laptop being the problem.

The accelarations may be still to high . try to decrease acc. rates again  .what is your drive system? lead screw, ball screw  ? what kind of stepper drive do you use?

I have the same type motors and the Xylotex as well. I use rolled ball screws on my shop made router with skate bearing on a steel track.
I recently noticed that I was getting some backlash from the Lovejoy couplings. The Gantry is very heavy @ possibly 150 pounds.
I had my motor on the X setup to run about 65 IPM at about 5.5 accel.
I swapped out the lovejoys for some solid couplers. I had to reduce my speed down to 38 IPM and 3.5 accel. No more backlash though. The machine was actually wearing out the rubber coupling in the Lovejoy.
To get my speed back up, I suspect its time to go with a belt drive on this. I feel the main reason for the need to reduce my speed was the slight misalignment of my motor to screw with a solid coupler. That should be negated with a belt, hopefully. 

Try 2 on the accelleration, I found that if you can't actually hear the steppers accelerate up then it's probably too high, I'd have to agree with rceebuilder there.

I have a lead screw with lovejoy couplers. The rubber inserts have been replaced by HPDE. I will try reducing the acceleration today as well as updating the Mach 3 version. The gantry uses skate bearings on a double steel pipe rail. I may need to remove the lead screw and test the friction of the gantry.

For what its worth, i DO think its your laptop.....

i have a homemade mill and was running it with my Dell P4 1.7 2GIG RAM. it worked fine up to 15 ipm, but anything over that and i would get occasional stalls. over and the stall were regular.

i "borrowed" my sond desktop on a whim and i can move all three axies at 80 - 100 ipm.

if you can get your hands on a desktop, Mach3 is a quick install and worth the test.