This coin is called a Liberty Head Dime or a "Barber" dime, after its designer.
Values as of 11/2009:
If there is a small "S" on the back underneath the wreath, it was minted in San Francisco and is worth at least $16 even in worn condition. If it's only moderately worn, that could jump to $145, and in nearly-new shape it might retail for over $320.
If there's no S under the wreath, it's a more common variety minted in Philadelphia. Its value would range from $2 to $60.