there are only two worth considering:
IntelliJ IDEA (best of breed, imho): www.intellij.com
Eclipse (almost as good, and free) : www.eclipse.org

your machine may have just enough memory to make the above feasible,
but i'd recommend doubling it to 256Mb at least. don't let your
hardware limit your ide  options; a good IDE will save you far more
time and energy than you could possibly spend on your PC :)

if you want something *really* simple, try:
JCreator LE (free, but quite limited): www.jcreator.com.

however, if you're doing any serious java  coding, you'll be far better
off with one of first two.