For the next couple of weeks, I'd have to say go with a single CPU system. This is because dual capable CPUs are always a cycle behind single CPUs and at the moment neither AMD nor Intel have a compelling dual capable chip.
AMD: Soon we will be able to get our hands on a 2600+ XP - while the dual capable 2200+ MP lags significantly behind in speed and costs about the same as the 2600+ XP will. Sure going dual 2200+ MPs will give you a speed boost in some programs but for most uses, the speed boost is far from being double. In fact, most programs only get up to 50% speed boost. So that makes the dual 2200+ MP system at roughly 3300+ speed in some programs (the rest will run at 2200+ speed). To me that isn't much faster than the much cheaper 2600+ single CPU system. 2600+ MPs will be out, but expect to wait several months - most likely not until 2003.
Intel: There is a 2.4 GHz Xeon, but I wish you luck in finding it. In reality you often have to settle for the 2.2 GHz Xeon (which is still on a 400 MHz fsb). The 2.8 GHz P4 on 533 MHz fsb will blow away a dual 2.2 GHz Xeon system in many programs. In the few that get a speed boost from dual processors, the 2.8 GHz P4 will be quite competitive with the dual 2.2 GHz Xeon. So I would rather spend less and get the single 2.8 GHz system. However: I expect the 533 MHz Xeons to be released any day now. If Intel goes all out and releases 2.66 GHz or 2.8 GHz Xeons, then I'd buy that instead.
Note: I often use dual CPU systems, my main computer is dual 1.7 GHz Xeon. So they do have advantages and I do recommend them, but the timing just isn't right today. My main program at work gets a 80% to 110% speed boost from going dual (yes it gets more than double the speed in some rare cases). For games, forget dual it won't help. For Photoshop, it will help a lot on a few filters, and do nothing on a lot of filters - so on average I'd expect a 25% speed boost (assuming you use a variety of filters). Honestly I've never used Corel Draw so I cannot tell you if it will be helped. AutoCad expect a 1%-12% speed boost if you only have one AutoCad session running at the same time. Expect a 70% speed boost if you run two at the same time in AutoCad.