If Bush thinks that sending "one of their own" through Senate confirmation will make it any easier, he's wrong. It will be a battle royale for the ages, unless Bush sends a pro-abortion nominee through. I do not expect him to do that.
I tend to agree that if Bush appoints ANY solid conservative, even a senator, the nomination won't be confirmed by this Senate. The one possible exception would be an appointment that would shift a seat from R to D, but even then, I don't think it would happen. My guess is that in the unlikely event of a SCOTUS vacancy, Bush will appoint a moderate, whether a senator or a judge.