CRC - Cyclic redundancy check.
http://www2.rad.com/networks/1994/err_con/crc.htm
This is basically a verification that when the data is extracted (installed), its all ok.
It seems very strange that both the CD and download wont work. The download is a common issue, CRC fails can happen all the time if your file didn't download ok, and with the CD - usually means there is a small scratch (or just needs a good clean).
Strange that it happens on both.
I would re-download from a different source just to double check.
