But how well/fast it works under the hood is another story all together. LR is a memory and disk access intensive program. XP was designed in an era when LR didn't even exist (far as I know).
Just try it.
tried it, my main system can be either W7 64bt or, by swapping a caddy, it boots in Win XPP 32bit on the same hardware.
Whilst W7 gives some performance benefits, you'd be pushed to notice it. These sort of small improvements are only significant to benchmarkers and magazine reviewers, in actual use you don't notice any difference.
It's also worth remembering that for a lot of the time LR makes no significant demands on system performance, it's only really when you start doing large imports or exports it becomes demanding of OS/hardware.
As far as Win7 or LR3 on the netbook, yes, that would be mad.
Actually LR3 works very productively on a netbook and all of them have W7 starter edition on them now. I wouldn't want to export hundreds of 5Dii images from mine, but for basic inspection of files, keywording etc on location, away from a big system it's hugely useful. This why I'm so sore about the lack of XP support or even being able to try
to install it, yes some bits might have worked properly, but nothing important to me.