At this price range, probably a Dell. If you mean boot time on first switching on the laptop, Vista isn't particularly fast I'm afraid, even on a well-specced laptop.
Something from the Dell Inspiron range should do, and they even come in pink. Try and get 2GB memory (might stretch your budget) if you're getting Vista and go for as fast a processor as you can afford obviously (T5000+). Personally I think it's worth stretching the budget a bit for the performance, but I would wouldn't I. The extra £100 or so is worth it when you think of life's other expenses.
Hope this helps.
Radderfire