I have BT4 dual boot with windows seven on my desktop,
what better party trick than to connect your already badass
nokia n900 to a laptop and boot up in BT4 for some security testing on your friends network (with his permission of course)


So I was thinking,

8GB microSD
Backtrack 4 Final/Pre-Final USB/Persistent Changes

using your n900 to "usb boot"


possible?

NeoPwn is a pen testing os being developed for the n900. Do some research on that. Maybe booting BT4 on the n900 isn't impossible, but it's very complicated and time consuming.

i wasent thinking of booting the bt4 distro ON the n900 but using the memory/or sd memory.. to hold a bootable distro of bt4.

so you could plug your n900 into a netbook via usb and select it as a usb on startup... make sense?

i believe i saw someone on youtube use the n900 as a boot drive, im pretty sure it was on a microsd card thought, it is possible though, ive seen it done........ yea here you go http://www.youtube.com/watch?v=pBCL50tJIKI

very do-able but may be also consider booting it inside the host os of laptop/pc using qemu and your phone as usb point

You could also consider chrooting to a disk image, Easy Debian style.

Alright, im going to attempt it

It's entirely possible, but IIRC, a FAT filesystem (such as the "Nokia N900" volume (/home/user/MyDocs)) will probably not work for most Live OS installs. If I'm not mistaken on that, then I'm guessing that was what killerjay was referring to, as formatting your microSD card as ext2 or similar is less problematic (for the average user) than reformatting the main volume.
But yeah, this should work fine. Just make sure the card you pick is decent (I wouldn't go under Class 4, and faster is better, of course). If you need to format the card as ext2, you can do that from the N900 command line (after installing the ext2 tools package, the name of which escapes me - probably e2fsprogs or something), or from a Desktop Linux install/CD, such as K/Ubuntu. It's not terribly complicated to do from the command line, but make sure you do it right, as you are messing with low-level disk commands, which can do Bad Things if you make a mistake.
Cheers, and let us know if you get it working.