Read the fine print (about the sale) on the main page of our site (http://dreamhost.com/). It's possible that we didn't update the signup code to be really smart about this, but you must pay with a credit card to get the deal. That's because this whole sale is actually a scam to get your credit card number - after the sale is over, all of your accounts will be disabled, and the Happy DreamHost Staff is going to take a day off to spend your hard earned money at the closest mall.
Just a general note to people posting about these issues....
1) read the main page at http://discussion.dreamhost.com/ if you haven't already.
2) If you /are/ going to ask for help here, and want any of the employees who come here from time to time to be able to take a look at your problem, please at least include your domain name, tech support ticket number, or web-id. If you don't want to post that information here, contact customer support.
That said, the actual problem here is likely some other sort of problem with the signup. Go to Billing -> Change Services in the web panel, and add the CDI plan again.
Write customer support about getting a refund on the Paypal payment and working out all the billing stuff. Not really my area of expertise, but it's something they can work out for you.
 Ok... not really.