You will need to download the latest versions of the following software:
Heimdal Kerberos 1.6.x.x - https://www.secure-endpoints.com/heimdal/#download. - According to the OpenAFS guide, MIT Kerberos has stability issues on Windows 7/8.
Network Identity Manager 2.0 - https://www.secure-endpoints.com/netidmgr/v2/index.html
OpenAFS Client 1.7.x - download page.