I'm not totally sure by car, but I'm sure it's not that difficult. On a map, it looks like you could take Interstate 35 almost all the way down. Don't know if that's the most direct route, but it loost like it will get you there.
http://maps.google.co.kr/maps?rlz=1C1DVCB_...l=en&tab=wl The road maps are good in Korea--things are labeled in English.
OR you could take a flight from Gimpo to Gimhae--Busan. And either rent a car, or take a bus to Geoje. People take a bus from Busan to Geoje all the time.
This page should be useful also:
http://www.gfra.net/travel___hotels_on_geojeHere's a hotel on Geoje Island that gives driving info:
http://www.admiralhotel.co.kr/eng/notice.d...um=1&page=2Hope that helps!!
Melisa