I always get very nervous before a race, but I do find that the more I do, the less nervous I get. For the first race of the year (half marathon in March) I'm usually a nervous wreck, but by Glasgow on 8/9/02 I'll have done 4 other races, and will be more settled at the start line.
So, yes, getting used to wearing a number and queueing for the loos is pretty much part of it, as is knowing just how many times you will want to go to the loo before the race, how your carefully tied laces are suddenly too loose/tight 2 minutes before the start and the dilemma you have as to whether to retie them, how far back in the pack to start, how many miles it takes you to settle into relaxed runnning, etc., etc., etc.
Give it a go, it will help you feel more at home on the "Big Day"