As far as Applet is considered from exam point of view these things should be made clear before appearing in exam
1.Restrictions imposed on applet when downloaded on web(Sun's appets FAQ gives you a good idea of that, i will say understand
all the points defined there ).
2.next important thing is , how will you talk to legacy system from applet
( consider all cases including
a. firewall present
b. firewall not present
I found pdf file in yahoo scea_j2ee group in file section to be useful.