Stepper motor problems

Hi guys, I have problems with the stepper motors, mainly on the y-axis, but also the x-axis. During fast printing the motors stutter, and i have tried to solve this by turning the trimpot-screws(on the arduino board) carefully clockwise, which increases power. Now however, I am having difficulties to hit the sweetspot where the motors are powerful enough to avoid stuttering, and also not overpowering. After i hit the homing button in pronterface, the motors gives of silent screams until it turn them off does anyone know how to help this?

one solution could be to change the maximum moving speeds in the firmware (marlin)
another could be to slow down printing speeds( which would be a little boring)

I'll ask on The IRC channel, and keep you guys posted on what i find.

My bed movement was very tight and tough, apparently one of the bearings was in very bad shape, and I have now replaced it and loobed the rods with bearing grease, which i can recommend. It is running much more smoothly now. I'm still a little uncertain how to adjust the the trims properly though but I'll try to get some readings from a voltmeter.

how do you first get a reprap machine and how do you get the print "fluids" to create another reprap and so forth?