Older software and hardware may be incompatible with Vista, but a lot of manufacturers have supplied downloadable drivers to make your printer and so on compatible.
Check online before you rule out Vista.
For sound, I'd buy a pair of Logitech laptop speakers for around �25, or use headphones, and make sure the laptop had all the other important spec I needed. Laptop speakers are mainly rubbish and at the lower price bracket sound is going to be low on the list of priorities for the manufacturer.
Unless you are a hard core gamer, edit videos or you are in to graphic design any of the �300 laptops will suit your needs very well. Decide what size screen you need; the size of the hardrive and so on, and shop around.
Tesco Direct is a good place to start.
If you need to carry it around a lot, go for a smaller screen. If not, get as big as you can find for your money