Round Rotherham Race. 50 Miles

I am doing the Round Rotherham like last year. I was wondering if anybody on the forum has done it before. I have a map and a route description from last year. But for the life of me when i try and load GPS info to my Garmin 305 for a breadcrumb trail from the instructions on their website i cannot do it. I am wondering am i thick {this is quite possible} or is it because i am using a Mac and the instructions are for PC. Can anybody help as the breadcrumb would be ideal for Recce as the course passes by my village.