Try running ZT alone for a while, see if it makes a difference. Also, before starting, clear out your cookies and temporary files. Maybe it will make a difference.
u last point makes great sense - every day before u start ZT/NOW/ODIN/Trade Tiger, clear ur cookies and temp internet files. this will reduce the clutter and also frees up some valuable resources in ur system. use a good system cleaner - if u cud not find any good sw then u can use ATF ( google it)
running ZT alone is not the issue. if u r accessing safe sites , then u can even disable ur av ( which is never recommended) . look at ur system and see what process is occupying most of the mem. if it is not so necessary - then just shut/kill that process. it frees up scarce mem resources and will run ur system optimal.
issue of ZT running slow - mainly is attributed to the speed of the net connection. look there also. try to use a wired connection instead of wireless connection. wired connection is far better than wireless connection specially in case of trading ( this u can test by viewing any youtube video - if it is buffering for a long time then ur net speed is low. try to improve there)
rgds
subroto