I know someone who has the Acer Linux netbook (Â£180?). Apparently, it is pretty good for most surfing but don't expect too much. It struggles with anything other basic web pages etc. You can't use a wireless dongle (because it is Linux) but it grabs any spare wireless bandwidth when it can. It has all the basics and battery life is about 3hrs.
I'm waiting for Windows 7 before I get one (should be released late this year). Apparently it uses far less system resources, so for a hardware-lite computer like a netbook you should get more out of it.
I have a Samsung N310. Didn't use it with Windows but instead put Linux on it straight away. I get circa 4 hours battery life out of it, I would imagine this would be similar under Windows. Its a good little machine and ideal for courses and sunshine tours.
If you want to buy buy now, windows 7 is due to be released and a lot of suppliers are trying to get rid of XP/Vista machines, so some good deals to be had. Tosh are good and reliable, Acer have come on in leaps and bounds, I have never been keen on HP/Compaq or the Ienovo (which was IBM)
Try to stay away from Vista, although most are shipped with Vista as standard they normally come with a "downgrade" disk (which isn't in my opinion). Reason being is that drivers work with XP and not all devices will work that well with Vista.
Alternativley wait for Win7 which I have been testing and it is so far an excellent bit of software and I haven't been able to crash it in the 2 months I have been testing it for work. I have also managed to get all our legacy systems working apart from a PDF driver, only downside is you will pay for being at the front of the queue
If battery life and speed matter to you then Vista/Win7 are not your friends. They push netbooks to the limit. I'd recommend Ubuntu Netbook Remix (UNR) as a straightforward alternative, the pre-installed Linux distros are pretty poor. That said, they can be cheaper than the same machine with Windows on (mine was) are are worth buying for that reason if all you're going to do is slap another OS on.