The goal: installation of BT4 pre-release on an external USB disk to create a portable lab environment with vmware.
The first step was to install BT4 on a USB disk. I booted on a DVD than used ubiquity to install BT on the HD. To prevent ubiquity to modify my MBR, I run this inside a vmware without disk!
Than I updated the kernel, installed vmware player and the nvidia drivers. I have to confess that despite all information on the forum I could not install vmware with the latest kernel. I had to roll back and everything works like a charm.
Another issue I found: I put all my virtual machines on a ntfs partition on my external disk. Bad idea: when having large files the ntfs process is eating all CPU. I put it on an ext3 and kept only a few gb for data exchange with other OSes.

I also found that when using KDE to delete files they are transfered into the trash but BT4 does not offer an interface to empty the trash. 2 solutions: you can modify Konqueror using the settings menu to delete instead or moving to trash or you can add a "link to Location(URL)" in the desktop and make it pointing to trash:/

A very convenient feature is to be able to mount the different partitions of the USB disk automatically in fstab using UUID. That works great. You can find the UUID of your drive running "blkid".

Now I can run my lab environment whatever the hardware I have.

Hope this help someone...