Fedora Hardware :: Java Application Stops Suddenly / Won't Even Start

I have these "out of memory" issues with fedora 13 64bit. previously we had centos5, the same environment in terms of programs used, nevr experienced these problems. the issues are for instance a java application already started stops suddenly, or won't even start.
example from tomcat stop:

[code]...

The one thing i don't understand about these numbers is where it goes all that used memory. i only listed the top 40 tasks out of 200 in order of physical ram used, can it be that even if it "sees" 5gb it cannot use it all, just like say windows7 and usable memory? (I recently troubleshooted that one, where out of 12gb w7 reported 8gb usable, I solved that by reverting the cpu overclocking.)