If you have not read the new document (September 2008) from the Congregation for the Doctrine of the Faith, you are really missing out! This is basically an expansion or updated version of JPII's Donum Vitae released in 1988 which includes some newer issues like stem cell research and other infertility procedures.
This has got to be one of the best things I've ever read! Truly, this is one of the reasons why I am so proud to be Catholic!
Please take a few minutes to read it. There are some hard things to consider...especially if you are struggling with infertility so you'll need to read it with a prayerful heart.