Alienware does have some awesome looking stuff and their custom-assembly is great for the lazy people, but it should be obvious that it's not the best stuff. You can easily find better stuff else where just as you can easily find better stuff there.
I'd say your best bet is to show him this thread, although any positive effect will be dampened by the insults... Although come on, it's not like they know who he is and it's not like he knows what he's talking about.