Run Windows off SD Card/USB 2.0

Could I run a full version of Windows off an SD card or USB 2.0? If I can, how would I? 

I want to do this because I want to remove my hard drive from my laptop because I don't really trust hard drives (because they have moving parts) and to also save battery. 

it will be so slow tho. USB rates.

yes as long as it shows up in the bios but laptop bios are not the most robust. .but its probably going to run slow. you could run linux with both of these methods or just a cd. just reinstall with no hdd and the preferred method.

why not just put an ssd in the laptop?

I don't think it would work. At least when in the past, Windows 7 wouldn't allow you to install on a USB device. I'd assume it would be the same for SD cards, but I'm not entirely sure.

I agree with this. Grab a 180GB or 250GB SSD, load it up with programs / OS etc, then store movies etc on external drives. If you want to install lots of games etc, you'll need a bigger drive (say 500GB) to allow for it.

I don't really want to buy an ssd for the laptop because I plan to download and delete lots of things on the laptop which will ware down the ssd quickly. 

Also, the laptop is an old netbook so I don't think it would be worth it...

I don't really mind the o.s. booting up slowly because I'll keep it in sleep mode most of the time. 

Honestly, given it's a small notebook, I'd just grab a small HDD for the OS etc, or a small SSD, and then grab a high capacity external drive, where all the downloads will be saved directly to. Thus, the netbook drive is preserved, and you don't loose the data if the drive does fail.