Best I could say is it'll run 2k8R2 as fast as a (in your case) E2220 with 2GB of ram will run it.

I have no idea of the performance characteristic of the OS, but I think RAM will be a limiting factor. Depending on what you're planning on doing with it at least. It should run fine for a low end low user-count SOHO box, which is what it was designed for anyway.
As far as CPUs go, it supports most E1xxx, E2xxx and E4xxx series, along with S775 Pentium D's and Celerons - you can check the validation details for the 945GZ chipset on ark.intel.com.
Keep in mind that it comes with passive cooling on the CPU, it's just a ducted heatsink, so you'll need to be careful what you put in there. There isn't an additional CPU fan header on the mainboard (there's a spot for one, but no header), but there is a single standard molex on the PSU (though I wouldn't be a fan of pushing that PSU with a full load). The biggest problem is there's not a lot of room for a HSF beneath the HDD that sits over the top of the CPU. Therefore, you're either sacrificing 1 HDD, or going with a low profile HSF which will still have airflow issues (pulling heat down off the HDD, and not a lot of heatsink surface area to work with).