Does anyone know how to import a rsa private key from a DER or PEM file into the CryptoAPI CSP?

I want to encrypt some data using a public key from the cert store (Which i have done), then decrypt it using the private key.

The problem is my cert does not have the private key, but I do have it in both a DER & PEM file, so just need to somehow import it into the app.

The MS API documentation is very poor, as it does not mention this senario at all.