start a new tab by clicking on the square next to the current tab, then you can type a new address...
if you mean you want a new tab instead of a new IE windows to open everytime you click on the IE icon, then i am not sure if you can do that at all unless someone can tell me otherwise
My Computer
Computer Manufacturer/Model Number
Viliv X70|Asus P8Z68 Deluxe|MSI FXA890-GD70
OS
Windows 7 Ultimate SP1
CPU
Intel Atom z520 1.33ghz|Intel Core i7 2600K|AMD Phenom II955
Memory
1 GB DDR2|32 GB DDR3|32 GB DDR3
Graphics Card(s)
Intel GM500|Nvidia GTX480|Nvidia 9800GT
Sound Card
Built in
Monitor(s) Displays
Built in Touch sensitive resistive lcd|Samsung 305T|HP 3065
It's pretty much the same way here in OPTION ONE of the tutorial below for Vista. If you set them like it is in the screenshot below in Windows 7, then it will open with new tabs for you.