I used Corel Draw a few years ago, when I was using a PC, but since then I changed to a Mac and now use a software program called "EASY DRAW". It's the easiest drawing program I've found and It does everything you'd want for making Intarsia patterns. I don't know if they have a PC version or not, I didn't see anything, on line, that mentioned it.
Attached is pattern I made of a truck that belongs to a client. Please do not copy the pattern unless you have my permission.