Well for folks like you there are only a handful of highlights you can easily ferret out by yourself - just read any guidebook and they'll clue you in - Venus de Milo, La Jaconde (Mona Lisa), etc. - note that entry later in the day is cheaper and this is for folks like you who just want to see the few mega sights - don't think i'm critical of your plans as i'm like you - rather bored by museums but want to see the world-famous stuff i've heard about all my life.

I did this in January. Wrote about it here:

http://makeashorterlink.com/?J2DA222AA

I've recommended it and also mentioned that some people didn't like it.

You buy your tickets at the Louvre. It costs extra (in addition to admission). Ask at the info desk and they'll direct you. I can't remember the details right now.

This is definitely not too basic a question. You're smart to plan your visit to the Louvre. It is such a huge and amazing museum-- the buiding's interior alone is worth gawking at. It makes sense to know which pieces you want to see and where they are. Because you can get lost in the Louvre (which might not be a bad idea if you have the time). I don't think you need a private tour, and don't even know if they are offered.
Many of the guidebooks (Rick Steves' in particular, and Eyewitness) will list their top ten pick of artwork in the Louvre, along with a suggested route to get to them all. With that list in hand, and sticking to the plan, you will still probably need at least three hours there. Then, if you want to make it a day, it's definitely worth your time to walk across the river and visit the Musee D'Orsay. Another must-do in Paris IMHO.
Trust me, even if you're not huge museum buffs, the Louvre is something else. Allow a half-day and you'll be glad you did.

Basic guided tour (Visite Decouverte) of the highlights is offered, from October through the winter -- Sundays at 11:30am, other days at 11am, 2pm, and 3:45pm. (The Louvre is closed on Tuesdays). Website: http://www.louvre.fr/louvrea.htm

The tour is an additional fee, and I advise making arrangements in advance, or at least several minutes before the tour starts. You go to the sign on the main level that says Acceuil Groupes/Tours Conferences. Tour Conference is what you want. You pay for the tour by renting a headset, because the guide speaks into an electronic microphone. You also have to leave a passport or credit card as a guarantee for the headset.

By the way, I've also recommended the Telegraph series here:

http://www.telegraph.co.uk/travel/main.jhtml?xml=/travel/2003/05/06/etlouvre.xml

You should find the article interesting.

If you want to do a "self guided" tour, you might consider picking up a copy of Rick Steve's "Mona Winks -- A guide to the great Museums of Europe". I've used it in Paris and Italy, and I think he does a good job of laying out a route through these huge museums so that you get to see the highlights, and gives some background and history in an amusing way. His Louvre tour is great.