Standard warranty is one year through most vendors. I had heard that microsoft had been accepting xbox's with the red ring of death passed the end warranty dates, however that was a while ago closer to when the xbox's were first released. I would recommend calling microsoft since you would have to call them regardless in order to have them send you the repair shipping label.
-edit: their site confirms that for a console with 3 flashing red lights, the warranty is 3 years for original xbox's

The warranty will continue for the remainder of your original warranty, or for 95 days after they return your fixed xbox (whichever is greater). However, if you pay to have it fixed, the automatic one-year warranty and the three-year Red Ring warranty start anew.