The Surface is using an ARM processor (Tegra 3). Meaning nothing made for the desktop will work with it until the software is recompiled for ARM. Some of it will take some tweaking or rewriting to make it work at all.
Microsoft will eventually recompile some things if they haven't done so already. Others may be a different story. Some probably will do it. But a lot will more than likely wait to see if the Surface is popular enough to mail it good economically for them to bother. In other words, if enough sell, expect more software quickly. But if not enough of the devices sell, don't expect some software to be ported soon, if it ever is.