A small variation to the formula suggested by cbatrody to make it work for even if there is a middle name also.....
=IF(LEN(A1)-LEN(SUBSTITUTE(A1," ",""))=1,MID(A1,SEARCH(" ",A1,1)+1,1)&" "&LEFT(A1,SEARCH(" ",A1,1)-1),MID(A1,SEARCH(" ",A1,SEARCH(" ",A1)+1)+1,1)&" "&LEFT(A1,SEARCH(" ",A1,1)-1))