ISU in St. Petersburg
At the below link is a street-level map of St. Petersburg in Latin letters. Check it out before you leave to begin orienting yourself to the city.
http://petersburgcity.com/map/index.phtml/z/bbdbppphppph
This link offers a wealth of information helpful to foreigners traveling in St. Petersburg.
http://www.oksanas.net/St_Petersburg_Russia_Guide/SG.asp#how%20can
This site, put together by the US Department of State, may provide answers for questions that you have regarding travel and general safety concerns in Russia.
http://travel.state.gov/travel/cis_pa_tw/cis/cis_1006.html
Check out the current exchange rate for the Russian Rouble.
(The amounts listed below the link are some round figures that may help when deciding an amount to withdraw.)
http://finance.yahoo.com/currency/convert?amt=1&from=USD&to=RUB&submit=Convert
2000 Rubles ($80 USD)
1000 Rubles ($40 USD)
500 Rubles ($20 USD)