How do you add a block

[d19rnyxx]

Hi I need to find out how I could add a block around my navbar ads

I want to achieve something like this
http://www.imagelnx.com/hosted/37d20682075ce118caad6637dab333a0.jpg

The ad sizes are 300x250

I would also be grateful if someone can link me to a detailed tut on how to make usersnames in the postbit larger

Thanks in advance for your help