Update the Korean Galaxy S
ICS or Jelly Bean cannot work on this particular phone due to hardware limitations, and many ROMS like CyanogenMod etc. are designed for the international version, not the korean version, thus you will have some problems.

My recommendation to you is to use KIES to go back to the latest Samsung released Gingerbread, root, then use a custom kernel (Tegrak is my personal choice) to get a lagfix. It will hopefully breathe new life into your phone. Hope this helps.

Also note there're many apps for Gingerbread that give you the feel and performance of ICS, such as Gallery ICS, Camera ICS, and ICS Launcher. Aside from being unable to run Chrome, you may not notice any difference.