hign cpu utilization in bt5 gnome-32

installed BT5-GNOME-32.iso on VirtualBox-4.0.6-71416. with 1Gb RAM & 1 cpu.
when start using it, the cpu on both guest machine & host are experiencing high cpu usage all the time (> 80 - 90%). checked processes & don't see any that really cause the high usage ...

anyone else having same issue?

Works on VBox 4.0.4 just fine for me.
Perhaps you should look to see what processes are running that may be using up all the resources.
Perhaps you should allocate more resources from the host.