vpngui.exe is a process associated with the VPN Client application from Cisco Systems. It is used to setup IPSec communications VPN clients.
Non-system processes like vpngui.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues.