I would think of it this way: Building Intel now, will basically ensure that you'll need to buy a new motherboard and cpu to upgrade in the future. Buying AMD now and you'll only have to upgrade your CPU. If you need the performance RIGHT NOW, build Intel. If you don't, AMD is a far wiser choice, both for your budget and upgradability.
I'm not so sure about that...
There's no guarantee that even AMD's next generation will give the performance that Intel delivers today.
If you look at the Core2 Quad series for example, and how long it took AMD to build a CPU that could beat it... Would you really want to wait that long? Core i7 was already out by the time AMD could finally offer something competitive with the Q6600. So wold you want to 'upgrade' to an AMD CPU with Q6600-performance by then, or just go for an I7 920 instead? (which again is a CPU that has been pretty much untouchable for AMD for almost 2 years now).