It's available for Windows as well!!
If you want to open the raw file in Photoshop CS3 (Edit in...) you can't because CS3 does not support CR5.4 but you can export as a tiff and work in CS3 as normal. This is what I do anyway so I'll stick with LR2.4 for now just because it's so much easier than converting in Phocus or Flexcolor. I'll do some checks as to the quality difference between the 2 workflows though.
The Camera Raw thing is a bit of a nuisance though, it is Adobe trying to strong arm users to upgrade to CS4, which IMHO isn't that great a version upgrade, I'm waiting to see what CS5 is like.