Hi kevin100...it's really up to you. I think you can register for co-op up until your next-to-last year of studies (ie. 3rd yr in a 4yr program, or 4th yr in a 5yr program). If your planning to enter a 4yr program and would like to do co-op during the summers (4month placements) you would have to take ENG 1EE0 this year soo you can find a job for the summer. If you're considering doing a full 12/16 month placement by taking a year off, you can take it anytime really. Keep in mind you have to be in your next-to-last yr to have placements longer than 4months.
IF you're thinking of a 5yr program (like society, or management...) you can still take it 2nd yr then do three 4mnth placements in the following summers after. Or again you can just do the whole 12mnth position. Those are just some options you can choose to do. You get the co-op designation so long as you do 12months of work in total related to your field.
If you decide to do co-op right after first yr, there prbly aren't a wide variety of positions since you just learned general concepts - I think you can get placements for the summer at Mac or Hydro One (those are just the ones I've heard of, there might be more).
The co-op websit is:
http://www.eng.mcmaster.ca/eccs/stud...op/engcoop.htm check it out for more info!