Firstly, you'll need to export the certificate and key from IIS, following the directions in this FAQ above. Secondly, you'll need to copy the PFX file to the Apache server. You will need the open-source OpenSSL tool installed (commonly by default on *nix platforms, and available freely for Windows). In the same directory as the PFX file you copied, use the following command, replacing the filename of your PFX file where needed:
- openssl pkcs12 -in -out pfxoutput.txt -nodes
Now you will have a single text file(named 'pfxoutput.txt) containing the private key and certificates. Open it and copy from the '-----BEGIN RSA PRIVATE KEY-----' line to the '-----END RSA PRIVATE KEY-----' line into another file - mykey.key. The rest of the file can be copied into mycert.crt. The two files can then be used in Apache.