I've found ladyalex's method will provide fresh looking tulips for about a week... maybe a little longer. However, along with the wrapping do this: Lay the bouquet on wrapping paper or newspaper, and cut the stems diagonally, removing about one-half inch of stem.
Re-wrap the bouquet in paper (making a cone shape) so that the tulips are standing straight. The tops of the tulips should not extend above the top of the paper although you�ll need to allow a few inches of stems stick out from the bottom. Place the wrapped bouquet in water for an hour or two, with the paper above the water line.
Re-cut the stems once more, before rearranging, again making a diagonal cut. Fill the vase with water, adding a floral preservative - a powdery mix of plant food and bacteria inhibitors available at your florist.
(We've used this process for a long time successfully, but it can be found in Backyard Gardener as well...)