Parking in downtown San Antonio?! What a nightmare. For the ceremony, there is valet parking at the hotel or there is a pay lot across the street. 

Parking for the reception will entail a bit of a walk. The venue is located above Pat O'Brien's but there is also an entrace from the street seperate from the restaurant/bar. There is pay parking a couple blocks away, either in the pay lot or in the parking garage for the Rivercenter mall. As shown here....

And just incase you intended to find your way from the ceremony to the reception....

Here are directions and a map from the Antonian to the reception venue.