M$'s big deal over the OS being tied to the original machine is mainly for the sake of who is going to provide support for Windows. With an OEM copy, the system builder is responsible for providing Windows support. So if the machine is replaced, then the system builder cannot be held responsible for any support.
Realistically, Microsoft does have a very relaxed stance of re-activitating licenses, just so you convey over the phone that you are keeping to one machine, one purchased copy of Windows, they will let you re-activate the license even if it's against their stated policy.
With the hardware requirement, it's a bit fuzzy and I haven't found anyone yet who understands it completely. First, the required hardware must be an integral part of a computer, like a harddrive or memory - a cd audio cable for example doesn't technically fit the requirement. My best guess is this - if you buy WinXP OEM with say a harddrive, the seller is guaranteeing that WinXP is fully compatible with that harddrive and will provide support if there are compatibility or usability problems. Still very fuzzy over what it all means. Bottom line is, Microsoft is not going to put up a fuss over the way these copies are sold as long as the end user is paying for a legit copy of Windows & not using a pirated copy. That's how Newegg can get away will selling OEM copies bundled with cd audio cables - they're getting away with the vagueness of the requirements, and M$'s just plain not caring to enforce strict policies.
And this hardware requirement actually can work to your advantage. If you buy a copy of Windows from a shady company who bundles crap hardware that doesn't fit the requirements, and for some reason the company screws you over, you've got some extra leverage to try & get your money back.