Wow, not too shabby. A couple of those look a little expensive, but overall, £497 is a pretty good deal for that setup. I'm surprised you didn't get 2 GB of RAM, though. But I'm not sure about your motherboard's compatibility.
Intel pentium 4 chip =£17 - good deal
asrock motherboard= £50 - ripped off by the guy richenstony was complaining about before
new case= £50 - expensive but it looks good
5.1 external trust soundcard = £50 - seems expensive to me for sure
philips dvd writer = £60 - that's the external one, right? I got one for around £40, but it's not too bad a deal
2Gb of RAM might have been nice but it was pretty expensive (DDR400 RAM).
It's easy to upgrade anyway.