I'm glad there is so much interest in KDE 4.1. I'm going to give this another try on a fresh system without any previously accumulated cruft.
In the meantime, I notice that the Debian lenny installer beta 1 does not boot in VirtualBox OSE as included in Debian. It freezes right after the "OK, booting the kernel ..." message. I had to run "install noapic nolapic acpi=off" from the boot prompt. (Perhaps you don't need all of these.) Does anyone know the reason for this? It'd be great if this could be fixed; otherwise using VirtualBox will become very annoying in the future, in my estimate.