I've talked about Multiple Core CPU Futures, but how about the dual core present?
The Athlon 64 X2 is now widely available in both OEM and retail* packaging, ranging from the 4200+ to 4800+. AMD just released a cheaper Athlon 64 X2 3800+ at under $400. As a developer, you will not find a CPU that compiles code faster. In fact, it's not even close. So what are you waiting for? You'll certainly need something to counteract VS.NET 2005's higher system requirements.
* The retail package includes, by far, the best stock heatsink I've ever seen-- it's a thin-fin aluminum affair with copper inlay and two heatpipes. If you can get the retail box for not much more than the OEM, it's definitely worth it. And you get an AMD X2 sticker, too. A STICKER!