I use this multi client and I find it easy to use :O its easy and you dont install anything or go step by step coding.
http://rapidshare.com/files/276783282/MultiWindow.rar.html
Open your PW game like your about to start playing and log on to your account. Unzip the file you downloaded then click on the Multi client and hit the ok's it brings up. Click on your PW launcher again and You should be able to duel log instead of it saying "client is running" and wont let you
lol sometimes it doesnt work for me but I think cuz I need to restart my comp to free its ram/cache/memory. but ya should work
just dont say you got it from me lol