I will be taking my mother[in warmer weather] to New York soon to see a Broadway musical. She is 75 years old and loves singing and dancing. She is also not a prude so an "off color" musical is okay. What would you recommend?? Also, how do I buy tickets ahead of time?

When you say that she likes singing and dancing, the four shows that immediately7 come to mind are:
42nd Street (a revival of the old Busby Berkeley musical)
Chicago (a revival of same show that became last year's Academy Award winner)
Never Gonna Dance (a Broadway version of an old Fred Astaire/Ginger Rogers movie)
Thoroughly Modern Millie (a Broadway version of the old movie)
Tickets are readily available for all four, so you can wait as there are likely to be discount offers.

Try for the Producers or Hairspray...

Check Playbill.com for discounts to these shows. It's free to become a member and you can get good discounts.

GYPSY! with Bernadette Peters!

You can hardly go wrong! Sign up at Playbill.com, broadwaybox.com, theatermania.com, etc., to receive e-mail notifications of "specials". Usually 35-50% discounts, sometimes 2-for-1, etc. Current codes are good through February, March...but new ones are announced all the time when the old ones expire.

Another good one is Wonderful Town. Also Fiddler on the Roof will be opening soon and Phantom of the Opera is always fun. ALso check Broadwaybox.com for advance sale discounts. Tickets are sold through ticketmaster.com or telecharge.com. You will not find any discoutns to Hairspray or Producers, but any of the others you might.

If she loves singing and dancing and doesn't mind a little more racy of a show go for Chicago. it is my all time favorite musical. the choreography of Bob Fosse is legendary and this showcases it beautifully. I don't know who is in it now, but i saw it with Bebe Neuwirth and boy can that girl dance!