The int parameter is the address of a buffer, in this case a FloatBuffer. You'll probably want to read up on them at java.sun.com, but here's a fragment to get you started:
import org.lwjgl.Sys ;
import java.nio.* ;
FloatBuffer v1 = ByteBuffer.allocateDirect(4 * 3).order(ByteOrder.nativeOrder()).asFloatBuffer() ;
int v1_addr = Sys.getDirectBufferAddress(v1) ;
The extra imports you may need are listed. The size allocated (4 * 3) is because you have three components (it's a vertex3
f) and floats are 4 bytes in size.
Most methods called on buffers will return a reference to the buffer itself, so you can chain methods together as above.
Hope that helps.