I would stay away from computer cords for power tools. They are only intended to carry 5 amps at the most. The ones I've cut into seem to be 16 or 18 gauge. I started to use one once as a replacement, but when I saw how it was built I changed my mind.
I would suggest looking on E-bay for motor cord (like SJOOW or SOOW). If you get a good deal on a bulk quantity, you can use some for cord replacements and also make up really good extension cords. I recently got a good deal on some 10/3 and made up a 50 foot extension cord for my welder.