Q: Wireless problems with 24 inch Imac

Since I have bought my 24 inch imac I suffer from several problems with the wireless system. First of all, very week connection (2bars, in comparison to 4 bars on my macbook). 2.) After waking up from sleep, it looses connection with the wireless network (I already tried some suggestions from Apples knowledge base without much success). 3. From time to time it loses connection at all (with a message. There is an error connecting to your wireless network). 4. Streaming music using my airport express is impossible. There are so many drop outs, it is impossible to listen to music anymore (it used to work perfect on my previous G4 and G5 imacs). I am using a ZyXEL P 660 wireless router as a base station. Thanks for any suggestions to this topic