What is the value of a one dollar with a distinctive o just over the DO Does this make it rare?

The "O" means it was minted in New Orleans. The value is going to depend on the date and CONDITION of the coin. Some mass marketers will hype the New Orleans mint because it has been closed since the early 1900's and even some new collectors are unaware it ever existed. Actually, in most years, coins from here are more common than those from the more well-known mints. You can get an idea of how to grade your coin here : http://www.coincentric.com/GradingMorganSilverDollars.htm You can get an idea of whether you have a rare or common date here : http://www.numismedia.com/fmv/prices/mordlr/pricesgd.shtml