oh you don't have to download it..

just go to "Google maps Street view"
and zoom in to a city and the extra Street view button should show up by the other buttons.

A little man icon will show up and if the streets are lined in blue then you can drop the icon in those places to look at the street view.
sometimes you have to double click for a new box to pop up also zoom in and zoom out
for moving around just grab and hold to drag it up / down/ side to side
click on the arrows to go forward or back

ahh found the help section-
[ Blue outlines show roads where street view is available.
This icon shows where you are on the map. The green arrow points in the direction you're looking. You can drag the icon to navigate to a different location. You can also just click on a blue outlined road to go there.
Drag the street view to look around 360°. Use the arrow buttons to navigate down the street. You can also use the arrow keys on the keyboard.

]
how they do it- special multi camera -
http://www.news.com/8301-10784_3-9724604-7.html