Lately since I've switched to Comcast broadband, I have trouble trying to connect to the Music store via iTunes. I get a message "Could not complete the music store request. The store may be busy. Check yur internet connection or try back later". I'm not having any other trouble connecting to the internet. One time I managed to get into the store but the scroll levers wouldnt work. Any ideas whats happenning? Im using an iMac with OS 10.4.3

You are 5 patch levels behind. You should seriously consider moving up to 10.4.8.

What version of iTunes are you using?

Do you have a router between your iMac and the cable modem? Some cable modems don't work right with certain packets when connected directly to a Mac. You can solve this with a router (which you should have anyway for protection).