There was a good vet-the-vendors article recently. The original article: "What Does It Take To Get a PC With XP?"
Here's a mirror of that (without the ads & crap) and with my highlighting:
Another no-ads version which will likely have even longer persistance:
Here's Slashdot's coverage, indexed to a particularly insightful comment:
Which leads to the question: If you're not big enough to have sufficient juice with M$ to get the products you actually WANT, are you big enough to warrant the attention of the Business Software Alliance? (Ernie Ball, Inc.'s experience)