Ctrl-Alt-Delete or right click on the taskbar and select task manager. there is a performance tab that gives you cpu usage, pf usage and memory usage. You can also see what programs are running behind the scenes with the processes tab. Look for anything out of the ordinary.
Have checked the running processes and no malware. CPU use is low when I run a virus scan and page file use rises slightly, although I don't understand why as there is still 1200 mb of RAM available for use. Is my system paging unnecessarily ? Also have noticed when I close a vmware machine and it releases RAM there is a slight stutter as memory is being released if I'm using another program. I have a toolbar on the desktop that displays RAM and as I see it ticking up after closing a virtual machine programs tend to lock then a second later start working again. Any ideas?