Check your gas cap. If the light came on shortly after a fill-up, it could be that the cap is loose. Although this is frequently the cause on newer vehicles, it's worth a look on your 2000 model.

Other than that, as RobertBrown says, you need an ODB diagnostic to tell you exactly what it is. With an older vehicle like yours, if it's not missing badly, could be emissions sensors. If it's missing, could be plugs, wires, coil packs, injectors. The "Service Engine" light is not something I lose sleep over, like an Oil Light coming on. LOL.