Easiest way to get from Louvre area to Chateau Versailles, RER C?

You're only about a block or two away from the Chatelets-Les Halles Metro-RER station. From there, you can take the RER B train south one stop to the St. Michel-Notre Dame RER station (on the left bank, right across from Notre Dame), then transfer to the RER C line out to Versailles-Rive Gauche. Don't forget to take that specific line C train, because it splits before you get to Versailles...the other train, the one you DON'T want, is labelle Saint Quentin en Yvelines. You could also grab a cab from your hotel to the St.Michel-Notre Dame RER station...it wouldn't be that expensive, and would avoid any confusion at Chatelet-Les Halles (which is a very big and very busy junction point) and any transfers.

Unless you have trouble walking, I don't think it's worth going to Chatelet and down to the deep-level Line B just to go one stop and back up to the shallow Line C. Cross over Pont Neuf and walk back along the river bank to St Michel-Notre Dame, it'll be a scenic walk.

I like Philip's idea of walking to the Saint-Michel Notre-Dame RER station.

If that doesn't appeal to you, for the least amount of walking take Metro line 1 from Louvre-Rivoli to Chatelet, Metro line 4 from Chatelet to Saint-Michel, and then walk through the connecting tunnels to the Saint-Michel Notre-Dame RER station.

RER C trains that go to Versailles-Rive Gauche will have the nameplate VICK on the engine.

To avoid standing in line, buy tickets in advance on the official Versailles Web site. Click on the link on this page.

Chatelet-Les Halles metro/RER station and "least amount of walking" are not appropriate in the same sentence :-)

I agree with you, Philip! That's why I suggested a route that only uses the Chatelet Metro station so there is no walking between that station and the RER station.

For another above-ground option, take either bus #21 or #85 directly from near your hotel to near Saint-Michel Notre-Dame.