What is a 2000 silver dollar worth?

If you're referring to a large coin that's really made of silver, its value depends on the price of silver at the current time. Silver has been in the $10-$11/oz range in late 2008 but can and does change a lot.

If you have a small gold-colored coin it's not silver obviously, and it's not gold either. It's an ordinary circulating brass $1 coin worth exactly one dollar.