That shipping method that you described is called # of Items vs. Destination.To set that up, go to System > Configuration > Shipping Methods > Table Rates Tab
Title: (whatever you want; ex. Ground Shipping)
Method Name: (whatever you want; ex. Ground Shipping)
Condition: # of Items vs. Destination
Handling Fee: (whatever you want)
Save your changes. Now that you have setup your shipping method, you have to specify the shipping rates. The shipping rates are setup at the website level. So, utilizing the Current Configuration dropdown box located at the top left hand corner of the screen, select the website (in gray and bold) that you want to specify the rates for. After the page loads, you should see a button that says Export CSV. Click, save and open the file in Excel. Make up your rate chart and then import the file back into the store and you should be setup.