I read that Santorum owed Specter for supporting him when he ran. And isn't Santorum going to be running against Casey (who I believe is very popular)?
Yes, Santorum owed Specter from his first race in '94. Good old Theresa Heinz whose husband held the seat Santorum now has, turned on Santorum (before she married Kerry or became a Democrat although like a lot of PA Republicans she was never any better than a RINO.) Specter came to his rescue.
And yes, Santorum is running against Casey whose FATHER was very popular (and Santorum is running far behind in the polls against the son.) Once Casey has to actually say anything, Santorum will improve his numbers because Casey could never be mistaken for his dad once he opens his mouth, but Santorum is in for a very very tough race and is iffy to retain his seat.