Water Skis

Can something you are wearing (like water skis for example) be made to float and not go under water? Or would it have to be a vehicle to act this way?

The attachment itself cannot be made to float, but a script in the attachment can make the AVATAR float. See:

http://www.lslwiki.net/lslwiki/wakka.php?wakka=llSetHoverHeight
http://www.lslwiki.net/lslwiki/wakka.php?wakka=llGroundRepel

Can I be piloting a vehicle and wear the skis to make the vehicle (and me in it) stay on top of the water?

I've seen pics of people in SL water skiing, so it can certainly be done...

Build a boat vehicle, and keep it fairly low-prim.

You would need a pose animation for the water-skiing position. Put a pose ball at the stern of the boat that positions you in the skiing position, aft of the boat, and script it so when that pose ball is sat on, the tow rope becomes visible. Make the skiis themselves part of the tow rope assembly, or make them shoes that the avatar wears. The latter would be better if you have a really good waterskiing animation, where the legs and feet move a bit.

You could have two versions of the boat. One where the person in charge of steering the boat is the skier, and a, optional passenger (or an alt) rides in the boat where the real pilot ought to sit, and one where the owner of the boat steers the boat from the normal position, while a friend skiis behind.