Updated:
check 27.3.2 Changing Subgure Numbering (page 78) of this file: http://www.ctan.org/tex-archive/info/epslatex.pdf
dont know how to get 1a, 1b.
i only know that using subfigure package, you can get sth like
(a) (b) (c)
Figure 1: Three Subfigures
