I keep getting the message coming up saying my virtual memory is low

No idea what that means

Have gone on to my add and remove programmes to see if there is stuff that i can get rid of, I seem to have an awful lot of Java stuff on there Java Update 5, Java Update 6 etc all the way up to 10 and then the J2SE Runtime Environment 5.0 Update from about 6 to 11, is it safe to get rid of any? Or is there something else i can do to free up memory?
Many thanks
