Its high time Republicans started backing candidates that actually reflect the core values of the party. There are plenty of great candidates out there, electable candidates. Why settle for anything less?
Given the probably run of Hillary, I really don't see conservatives swinging the vote over to that side of the aisle. Many conservatives disagree with a lot of Bush's policies, but still voted for him because he was the conservative candidate even if some of his policies, such as No Child Left Behind, left a sour taste in their mouth.
I find it hard to believe that conservatives would stay away in droves on a Giulliani/Rice ticket and tip the balance over to Hillary in '08. The distasteful idea of her in the office, and the conservative ideals in other areas, should make the ticket winnable. If pro-choice/pro-life is the only voting issue and both tickets sit on one side or the other of the issue, you default to other voting criteria. In this case, a lot of pro-lifers would default to other conservative ideals, and the vote should fall Republican in that case.