HI Gedi,
I have just posted on performance issues with vCenter myself.
I have discovered that the tomcat service "VMware Virtualcenter Management Webservices" seems to eat resources, http://communities.vmware.com/thread/241102?tstart=0
Try stopping this service and see if it improves, you can set the startup type to manual so it can be started if required.
This obviously stops web access and the performance overview page on performance tab will not work but performance details are still available.