Yes, it's a new OS - BackTrack 3.
Running of a USB stick on a 1.5Gb FAT32 partition, with persistent changes on a ext2 partition. Runs smoothly, feels very responsive and fast - we'll just have to see how well it does on the "aggressive security" part...
Installation went suprisingly smoothly. I had found a SanDisk Cruzer 4Gb for cheap, and used PartedMagic (mentioned in my last post) to divide it into two partitions - one 1.5Gb Fat32, one Ext2 covering the rest of the avilable space. Once I had downloaded the USB Extended version of BT3 with my desktop, I mounted the ISO and copied the files onto the fat32 partition. Then I just ran the provided .bat file to make thestick bootable. Switching over to my Eee, I created a folder named 'changes' on the Ext2 partition, and edited the syslinux.cfg file as outlined in an article on eeeuser.com's wiki. Then it was a simple matter of rebooting my Eee, selecting the correct mode to allow for persistent changes and wait for the boot to finish.
Boot times are - compared to the native Xandros running of the SSD - fairly long, but still a lot shorter than my desktop. I've yet to find my way around very well, and I haven't had a go at accessing the agressive security features yet. Expect a short post on that once I gotten around to testing it.
So now my Eee has three operating systems to choose from: Xandros (both Easy and Advanced Mode), XP on a SD card, and BT3 on an USB stick. I might reuse the stick for otehr distros later, or see if I can't manage to set up multiple OS's on it. Time will tell.