mcavana,
I just did my first century last weekend. I didn;t ride for a week and a half before. And I was in New Orleans partying it up, and eating A LOT! (acutally gained 5 lbs. on the trip). I had no problems at all on my ride. Legs felt fresh, and I didn't struggle much until the hill they threw at us at mile 80. And even then I was passing people... you should be fine...
If anything, jsut do a couple cruise around rides to keep yer legs moving.. but don;t push yerself at all... If you tire out yer legs before the century, you'll be hating it!
jeff