Even though you have tried swapping/removing ram, The errors do sound like a ram issue. have you tried testing your ram? you can try this one
http://www.simmtester.com/page/products/doc/docinfo.asp
I think that i did need to enter in my e-mail address and some other info, but it was the tester that I used to confirm that i had bad ram. Also note that it might not be bad ram as much as a bad ram socket.
Other things for you to also try is to clean out any dust in your case, because sometimes dust/dirt can cause interference that can cause the crc errors. the only other thing to do is to run scandisk or something better (norton utils?) to check that your hd/partition info isn't a little bit off.
A side note is that all of us could be wrong and some sort of virus/spyware/corrupted program is causing these errors.