Go to Window > Preferences > MyEclipse > Application Servers > Tomcat 5 > JDK Then under Optional Java VM Arguments, enter in
-Xloggc:log.gc
I noticed that you had typed -Xlogg:log.gc. I’m assuming that is just a typo but I wanted to just make sure.
You don’t need to put the -verbose:gc argument since the -Xloggc:log.gc option overrides it. If you just use log.gc as the file name, that file will be generated in tomcat’s /bin directory.