Here are some common problems when using linux in virtual box
1. Sound sometimes does not work
2. (for macs) Isight does not work.
4. Regular settings.
5. Compiz problems
OK, so lets start at sound.....
sound is a common issue in all variations of linux.
There is a work around. By killing pulseaudio and restarting it, you can get sound working.
Tell linux at startup to kill pulseaudio. IF you need help post here and i will give you full directions.
For most just add a usb filter with the webcam. Then install the drivers.
3. VPN... this is a big issue. It usually takes some time to do this. I have found the best way for this.
download cisco vpn for linux and install
install vpnc in synaptic
download this and install for gui :
4. virtual hard disk space, ram...
you should give a good amount but less than half because the host has to support the guest.
5. Compiz issues.
If compiz does not redraw the windows try addong the compiz icon and when this happens restart compiz
Hope this helps some