In Corel, draw a series of parallel lines for the "pocketing" toolpaths, and put them on a seperate layer. Trim the lines at the letters. Import into Mach3, set up your layer depths and route. You might have an easier time by just exporting the text, and using a CAD program to draw the pocketing paths. A9CAD is free at
www.a9tech.com
Also, download LazyCAM at
www.machsupport.com , it's Mach3's new importer. Watch the video too.