I've just ran a job which is fairly large and feeds are pretty quick, and if i scroll or pan the view window the program goes bonkers loosing position and halting, after a few seconds it resumes but has lost position.

The comp is a p4 with 2ghx proc and 1gb of memory.

Has anyone come accross this before, and is there a cure.

I'm putting it down to the speed of the comp, any suggestions.

There is a history of problems with the video window and running extremely long GCode files and I think it is probably more to do with the PC’s video card than it is to do with processor speed. However, turning off the video window (Diagnostics / Toolpath on/off) seems to cure the problem others have found.

Tweakie.

Don't click in the toolpath window while the machine is running. It's a limitation of Mach3, not your PC.
And as Tweakie said, I'd turn the display off if your have more than around 200,000 lines of g-code.

sorry for the late reply guys, thanks for your help.