I've not tried that myself but you used to be able to supplement your PC's ram with USB mem sticks on XP I think. Although ram is fairly cheap now so I cant see why you'd really want to.
It does work mate, but only really useful if ya have a low end system. I used it on my naf pc world netbook! it did work, but upgrading the ram worked ten times better!
I don't know what the first set of instructions are referring to(?), but the Windows 7 instructions are referring to Ready Boost, and it is incorrect - this isn't about adding RAM, it's about using the USB drive as a hard disk cache. This is available in Vista onwards. Info at http://en.wikipedia.org/wiki/ReadyBoost .
I use it sometimes on my Samsung netbook. No point if you have an SSD, like I do on my laptop.