The GS500F (2004+) is a fully faired bike. It is possible (with a little bit of effort) to install a F model fairing on an older unfaired bike. Other options include:
2000 GS500E with Spec II fairing (courtesy of gstwins.com member Rick Sonderfan)
TCP Aerodynamic Body Kits for SUZUKI motorcycles are not available for aftermarket distribution in the U.S.A.
GS 500 E Eliptical Fairing from TCP's product page
2001 GS500 with custom painted Airtech Titan fairing (courtesy of gstwins.com member Chuck)
If you happen to dislike the looks of faired version (not an uncommon thing BTW!) then please read this topic about converting faired 500F to naked 500E.