Unless something has changed, if you want to get off the ship in St. Pete independently, you'll need a Russian visa which takes time and $$$. For an August cruise, you will be pressed to get a visa. See the State department site ( http://travel.state.gov/travel/cis_pa_tw/cis/cis_1006.html#entry_requirements) for all the painful details. The ship's visa covers you on all Regent excursions as Jim states.
Scott
Ren R7:'01
HAL Volendam:'02&'05
RSSC Mariner:'02,’05,’09
RSSC Voyager:'03,’05,’06,’07,’08,’10
RSSC Diamond:‘04x2
RSSC Navigator:’08
Silversea Spirit:’10
12:A&K Le Boreal,Antarctic; Voyager,Iceland
13:A&K Le Boreal,Arctic
| 
