In Cozumel, Is there a beach you can walk to from the ship?

Yep...right next to the International Cruise Ship Terminal is the El Cid/La Cieba Resort which has a nice, but small beach. Good snorkeling, nice hammocks, good drinks. Please do not litter and watch out for scuba divers entering and exiting the water. Also, go further in town if you wish to buy stuff, the prices nearby are highly inflated.

We arrived at the Langostura pier instead of the International pier and there was not a beach but there was front, of course. i don't think it matters too much...just rent a car and you will be on a beach of your choice (we looked for 20 min) in no time.

Personally I wouldn't rent a car. Remember the people in Cozumel want to do WHATEVER they can to make sure you're having a great time. Get off the boat, as one of the cabbies to take you to the nicest closest beach and they'll be happy to do it. And it'll probably cost you 5 bucks!

I think the best way to see Cozumel is to rent a car. I did it and we had a blast. There are no boogeymen in Cozumel...

I have been to Cozumel a number of times, and have rented a car and taken taxis. When we stayed in Cozumel we rented a car and toured the island, very easy to do, just remember to gas up before you return it. Higher gas prices than you will be used to but way better than what they charge when you turn the vehicle in NOT full.

But my favorite thing to do in Cozumel when stopping for a cruise is to taxi to Paradise Beach. Very nice beach, kept very clean, a nice young Canadien guy Tom runs the place. They have plenty of beach chairs, water sports for the kids, good food servd in the restauraunt, or at your beach chair (MY FAV).
The waiters are very attentive and easy to get a taxi back, and lockers are available. MY next favorite thing is the outdoor showers. To enjoy the beach all day, and then not feel allsticky for the ride back, and shopping in town is wonderful. I always bring some travel size shampoo and soap.
check this link
http://www.paradise-beach-cozumel.com/

I too was going to suggest Paradise Beach while in Cozumel! We loved it. It was great...good food, chairs, umbrellas, watersports, bungee trampolines. There was also the bar Carlos and Charlies right next door! We all had so much fun there...in fact we are going back when we sail there this spring break!

How long of a ride is paradise beach from the pier?

It depends on the pier. There is more than one. But generally I'd say 10-15 minutes by cab.