The bootable USB with Linux on is pretty simple to do. You need to download 2 things, a program to make the USB drive bootable, called Disk Imager (it's tiny.. like 30 or 40k i think) and the .img (kinda like a .iso) of the linux distro you're after.
For ease of use, i'd suggest Ubuntu's Netbook Remix designed specifically to remove all the filler for low spec low battery machines. Find it
here. Installation is horribly, horribly simple via
here.
Most importantly though is, you dont
need to install linux on your laptop at all. Throw the USB stick in, boot up, set the boot option in bios to USB (name of the drive), then when it loads the menu screen, select "try Ubuntu Netbook Remix". It's a fully working operating system running right off the USB drive, without making any changes to the laptop itself. it has media players and instant messengers and all that jazz. Use the leftovers of the USB stick for your movies and you're set!