Hi
I installed a base archlinux system then installed xorg and kde trunk via these repos:
http://bbs.archlinux.org/viewtopic.php?id=44507&p=1
They are daily snapshots of the svn trunk

I can log in via kdm but the system freezes after it hits the Desktop. The freezes also differ from time to time, sometimes it freezes after it has loaded the tray icons, sometimes before that, well actually I only saw the tray icons once.
I already deleted my .kde folder but that wouldnt fix it.
Also it looks like every time I start kde, the desktop load process seems to get a little bit further but it still freezes in the end.
1. boot: no panel/no background ->freeze
2. boot: panel/no background/plasmoids all over the desktop, battery plasma stretched in the upper left corner ->freeze
3. boot: panel/background/battery icon at the right place ->freeze
....

I thought about asking on the archlinux forums but since this distribution is very minimal and the kde version is straight from svn I figured I could ask here as well plus I already registered here

oh I use virtualbox, but doubt that's a problem

I have no experience of Arch but a possible culprit for freezes could be lack of space.

KDE 4 also uses ~/.kde4 not ~/.kde ( unless you use Kubuntu Intrepid )
How much RAM ( virtual machine swap too please ), and hard drive space did you provide the virtual machine?