I was having some difficulties getting BT5 64-bit KDE to install in VirtualBox and after hunting around on this forum I figured it out, so I thought I'd share.
First, as pointed out in other threads, upon booting BT5 and running startx, KDE fails to load and you get kicked back to text mode. To get KDE to start, you must first do this:
This fix was previously pointed out here by fnord0 (and many thanks to him).
After KDE boots, you can run the install script on the desktop without incident.
Upon reboot, startx will again fail. To fix this we have to take an extra step:
Next, to install VirtualBox Guest Additions you need the kernel sources by doing:
This was originally posted here by muts (and again, much thanks).
cp -rf include/generated/* include/linux/
After the kernel sources have been prepared, the VBoxLinuxAdditions script will run without incident.
After all of that, BT5 should be good to go. In the event startx fails again, simply repeat those 4 'rm' commands in step 2.