In minecraft version 1.2.5 and probably the versions before and after there is a glitch to get above the nether in survival.

Steps
step 1-you have to dig up and around until you find a place where you are at y-126 (the highest point in the nether)
step 2-get an ender pearl
step 3-Through the ender pearl up at the bedrock
step 4-jump until you are above the nether

When you are above the nether you have an endless building space that goes 128 blocks up and is most likely not grief-able. There is a chance you will get banned on a server but don't yell at me. This is just cool because it's an endless place were monsters don't spawn and you can build endlessly.

If you are on a multi-player server and do not wish to get hurt you can also use a door or blocks in place of you. to use the door method you need to find an area at y=126 in the nether where there enough room to place a door and stand inside of the door. When you are inside the door log out and then log back in. this will place you on top of the nether since minecraft forces a player in danger when not online up to the nearest safe point.

If you wish to do this with blocks you need to people.what you have to do is get to the highest point in the nether and log out. While you are logged out your partner has to place blocks where you are. when you log back in you will be on top of the nether! This happens because of the same reason as the door method.