I was recently in the same position and ended up going for a Dell. PC World are a nightmare unless you agree to buy one of there overpriced and unneccesory warranties. Only go for a MAC if you are familiar with them and need to use them for Video/Music (I don't want to start a mac v pc debate - i work with computers for a living and Mac's are good for certain things and the look pretty but are not really the best way forward for the majority of people).
Dell were effecient and the machine is seriously good value.