Just thought I would pass along some info in case someone is pulling their hair out trying to get static IP addresses working inside of VirtualBox and having problems (I ran into this in OpenSuSE 11.4 inside of VirtualBox 4.0.12).
By default, all VM's inside of VirtualBox use NAT for their adapter configuration, which works fine for DHCP assignment, but not for static IP assignment (since NAT usually assigns a completely different network and IP address).
To solve this in OpenSuSE 11.4, I went thru the usual setup for networking (hostname, static IP, netmask, default route/interface, DNS, etc), but I changed the adapter configuration for the VM itself from NAT to Bridged. Saved everything, restarted the box, and walah, it works
This can be used when you want to utilize your own network and the gateway of your router, and works well if you want to host your own (whatever).
If anyone has more info, please add it...