Romans 9 is such an alleged stronghold of truth for Calvinists.
Here in the Quick Answers to Calvinists Format is addressed Paul's quote that God has mercy on whom He wills, and whom He wills He hardens and Does not the potter have power over the clay, from the same lump to make one vessel for honour and another for dishonour?
Romans 9:17-23

Just as Paul is pointing to God having mercy on whom He wills in righteousness by having said GOD SAID TO MOSES in Romans 9:15, so here with Pharaoh and his confirming use of 2 DIFFERENT Greek verbs in R9:22-23, Paul is pointing to God hardening whom He wills also in righteousness. The potter illustration involves Gods work in the nations and not salvation.

Here is a link to Paul's Conditional predestination explained - as written in Romans 8:
http://www.youtube.com/watch?v=iFplZVAuE_E&feature=channel_page

Here is a further expansion of Romans 9:22-23
"Romans 9:22-23 versus Calvinism - Jacques More"
http://www.youtube.com/watch?v=GefhpH6zQSY&feature=channel_page

If you would like to know more about Jacques More and his writings go to www.jarom.net