I don't speak Polish, but I think I know pretty well how to pronounce these names:
Waclaw sounds like WAT-suahv (I can't write the L with the line on, but it sounds a bit like the English W).
Grzegorz - GSHEH-gawrsh
Szczepan - SHCHEH-pahn (first sh as in shine, then ch as in chin)
Swietomierz - I think it's something like SCH-wyahn-toh-myerts (the first E is nasal, a bit like "un" in French).
To all Polish-speakers out there, sorry if this is totally wrong! But I did my best!
Does the sea exist
Because of our longing?
My PNL
http://www.behindthename.com/pnl/3258/61573