How do you make an object transparent only on one side?

My apologies if this is already covered, but I want to make a window that can be seen out of, but no one can see inside......

I can make transparent textures no problem, but this one is stumping me...help!

There are two ways to do this. If you drag and drop a texture from your inventory onto an object it will apply only to the surface of the object it's dropped onto. Alternately while you're in edit mode click the checkbox next to "select texture." That allows you to click on individual surfaces and edit the texture properties for just that surface.

Hi Merlot

Select the different sides of the object separatly, putting a transparent texture on the one side, and a solid/opaque texture on the other.

How to do it:
When you are editing your object (in this case your window) you will see a set of options with tick marks or radio buttons in the top section of the edit box. (By default "Position" is selected.) Choose the "Select Texture" radio button.
Now when you click on your object, the only texture selected is the side that you clicked on. This is indicated by a white circle with a cross in it. You can now go to the Texture tab and put your transparent texture on. Now select the opposite side and add the opaque texture. Done.

The reason this works is because SL only draws the face of the object that you are looking at, so when you are looking from the opaque side you can't see through. When you are looking from the transparent side however, the away facing solid side is not drawn, and therefore you can see right through.

Edit: What Chip said. I really need to learn to type faster

hehe, I cheated. Your answer was more thorough

A million thanks to ya both, I totally understand this now! Woo Hoo!