Currency:

Currency may be exchanged at a currency exchange office (recommended), as well as in hotels, banks, and at the airport.
Credit cards (Visa Card, Master Card, Maestro) are accepted in hotels, restaurants, and shops. The country has an extensive network of ATMs.
The best way to check current exchange rate of Polish zloty (PLN) is to go to website of the National Bank of Poland: http://www.nbp.pl 

Visas:

In December 2007 Poland signed the Schengen Treaty. There is no passport control at the borders of the entire Schengen zone. Nevertheless, an ID document (ID card or passport) is required when crossing the borders.
Citizens of some countries are required to obtain a visa prior to coming to Poland. YOU ARE ADVISED TO CONTACT THE POLISH EMBASSY OF YOUR COUNTRY TO GET FURTHER INFORMATION ABOUT THE VISA REQUIREMENT.

Weather:

Poland is a country with moderate climate, transitory between marine and continental. In July (summer time) temperatures fluctuate between 20°C and 30°C. Mornings may be chilly, rainfalls are possible.