Madcow is another term for the Bill Starr 5x5 right?
I'll talk about setting up your training for the final days in a second, but the most important thing you'll need to do before your first meet is get an idea of your openers. Your opener should be a weight you could hit on a day where you wake up with the flu, pull your hamstring getting out of bed, and find out your dog died last night. In other words, you should be good for your opener on your worst day, that way you know you will get it no matter what. That also ensures you get a total, and builds confidence for the lifts to come. It doesn't matter what you open with, it matters how you finish. Here's a couple great resources opening choosing openers and attempts:
http://www.elitefts.com/documents/openers.htm
http://www.usapowerlifting.com/newsl.../features.html
Have an idea of your openers before you even show up, but you won't finalize them until you are warming up and see how you feel. Unless your meet director wants the openers early for some reason, if so just be conservative. It's much better to smoke your opener and make a slightly larger jump than have to grind out an opener and be toast afterward.
Now, about setting up your training. For this, I need more information. I assume since you are using a Starr routine, you are past the novice stage, but correct me if I'm wrong. How long have you been seriously training the squat/bench/deadlift? What are your current numbers on your work sets? What weight class will you be?