headlamps from 97-00 bmw 5 series should be interchangeable amongsts each other since it's the same headlight style. so that should fit. i think you can also interchange(with very little to no modifications needed) any 5 series (minus the X5s)between 97 and 03 since it's the same body style.
so you can even outfit you 98 with angel eye xenon lamps, you'll just have to do the wiring for the angel eys/xenon (if you're switching from halogen to xenon)