How can I import sounds from a keyboard to GarageBand?

Is there a way to play other instrument sounds besides the ones in the GarageBand Software?

you can download any of the thousands of SoundFonts avilable online:

http://www.bulletsandbones.com/GB/PlugInsSoundFonts.html

or buy one of Apple's Jam Packs:

http://www.bulletsandbones.com/GB/PluginsApplesJamPacks.html

My Korg has a sound bank with tons of sounds that I would like to import.

there is no way to "import" the sounds your keyboard has, but you could plug it into the line-In on your Mac and record the audio

Also, I have sounds that I have sampled from records that are mp3, can I play those with the MIDI keyboard?

you can build an instrument within GB:

http://www.thegaragedoor.com/tutorials/building.html

How can plug my KorgX5D into the inline on my mac, so I can play its sounds live?

use the line-out, or headphone jack on the keyboard.

I have a MidiMan 4x4

you can only play sounds installed in GB through a midi connection:

http://www.bulletsandbones.com/GB/GBFAQ.html#Audionotmidi

the Logic series of software, among others