Aren't there already CRC32 classes out there you could use without reinventing the wheel? e.g. Google [.net crc32 class] yields http://blogs.msdn.com/b/delay/archive/2009/01/14/free-hash-a-reusable-crc-32-hashalgorithm-implementation-for-net.aspx , amongst others.

If there is any security requirement to what you're doing you'd probably be better off using an SHA hash. MD5 is now considered broken for serious security purposes.

http://msdn.microsoft.com/en-us/library/system.security.cryptography.sha1.aspx