I've never tried knife blanks, but I don't see how it would be a problem at all (just slow). Check out the earlier videos from Grimsmo Knives on youtube - they started off with the exact same mill and used it to make blades before getting a Tormach. https://www.youtube.com/watch?v=RCGbiytmJ4A
I use Mach 3 - the computer is just one I threw together from used parts I had floating around. ~5 year old Athlon 64 with 2GB of RAM.