Well I've had a good night's sleep, so I should get things right.

I didn't manage to read the Samsung page John linked to - some problem with Firefox settings just flashed it on screen - but if the F9 trick allowed you to boot from USB you don't need to worry any more about changing BIOS settings. Looks as though your Phoenix BIOS is a stripped-down version, so you probably can't do anything about that.

To answer your final question first - when Ubuntu is running from the USB ('Live') the essential bits of code are located in memory and the system reads other bits of code from the USB drive as needed. This is easier for Linux than Windows because Linux is much smaller and the code is much more modular.

As for saving files, you can save to a partition on your HDD - Ubuntu should recognise your Windows C: drive (it will probably identify it as 'sda1' - the D: drive will probably be 'sda2'). With Ubuntu running live, you can save to either.

If you install Ubuntu to sda2 (D:) Win7 will not be able to read files saved there unless you install an additional Windows utility (I use ext2IFS) because it will be formatted as ext4, not FAT or NTFS.

And finally, if you install Ubuntu, it will install a bootloader (probably GRUB2) which will give you a menu to choose Ubuntu or Windows when you boot. This happens after the BIOS has done its thing, so again, you don't need to worry about altering the BIOS or hitting F9.

I'll have to leave it to those who know Ubuntu to sort any detailed questions, but with recent Linux installation programs you are generally safe in accepting defaults if in doubt. The most important choice is at the beginning - which partition to install to. Make absolutely certain that you don't choose your Windows partition - the installer should identify it, and you can also tell by the size. If you make a mistake in this, your Win7 install will be wiped out.

Don't worry too much - it's usually fairly clear if you give yourself time to think. I've done about 100 installs, and not made that mistake yet.

Phil