If each cell is only two names (first & last, no "Jr.", etc.) it's
pretty easy.

Dim c As Range
Dim rng As Range
Dim iPos As Integer
'change next line to suit
Set rng = Sheets("Sheet1").Range("A1:A10")
For Each c In rng
iPos = InStr(c, " ")
'extract last name and put in col B
c.Offset(0, 1) = Right(c, Len(c) - iPos)
Next c

Hth,
Merjet