Update: 2013 06018 - I had to do 50 conversions today, so I have attached a shell script to to automate this process.
You have a pkcs12 bundle with a private key and certificate in it - in this example we will use a file called www.website.com.p12. I use SimpleAuthority as it is cross platform and the free edition lets you create up to 5 keypairs, which is plenty for the lab...
You don't have a password on the private key (passwords on machine loaded keys are a waste of time IMHO)
You have a Linux / MacOS X / Unix system with openssl installed (Mac OS X does by default, so do most Linux installs...)
3 commands you need:
First we take the p12 and export just the private key (-nocerts) and export it in RSA format with no encryption (-nodes)