Why not go for a company that is renowned for quality, such as Dell?
If you want the best possible deal, and have a list of specific components you want, it may be better to custom build. But you'd be on your own in terms of support - this suits many people though.
Remember most brand names use standard components, the only thing that is branded by them is the case. So as long as you don't mind spending a bit of time doing it, building your own is a good way to go. If you do this, don't buy any components until you are ready to buy the complete PC - you will then save on postage costs, and components generally reduce in price over time anyway.
I recommend going for a couple of hard drives - that way you can have your data on 2 hard drives (OK, this isn't a foolproof backup method, but it does protect against hard drive failure and if that occurs you have an instant backup).
I also note that the specification you link to doesn't go into detail, like they say the HDD is 7200rpm (very standard these days for IDE) but that is meaningless without the interface, access time etc. On board sound? Not ideal. What interface does the video card use? As for the RAM, "DDR 2" is almost meaningless out of context.
I see that it's a dual core CPU - but will you be running a lot of CPU-intensive multithreaded apps? I bet BVE is single threaded (can anyone confirm?), and I know MSTS is.