virtualbox.org

Hi all! I'm using latest VBox edition (3.0. under M$ XP running a Debian virtual server. While updating the packages from the Internet with aptitude or installing new ones my host machine completely slows to the point it is unusable with 99 or 100% CPU usage. My hosts is a Pentium 4 - 2.8GHz with 3GB RAM.
Is this normal or I'm having some issue here ?
Thanks in advance for your comments.
Limaunion

Guest settings?

Here're the guest settings:

System:
Base Memory: 256MB
Processor: 1
Boot Order: Floppy, CD/DVD-ROM, Hard Disk
VT-x/AMD-V: Enabled
Nested Paging: Disabled
Display:
Video Memory: 12MB
3D Acceleration: Disabled
Remote Display Server: Disabled
Hard Disks:
IDE Primary Master: Debian5.0.vdi(Normal, 8.00 GB)
CD/DVD-ROM: Not mounted
Floppy: Not mounted
Audio: Disabled
Network: Adapter 1: PCnet-FAST III (NAT)
Serial Ports: Disabled
USB: Disabled
Shared Folders: None

Let me know any other information you may need.
TIA.

What if vt-x is off? or apic on?