Heather, I'm not a legal expert, but from the information I found I think the parent with sole primary care is the same as a custodial parent.

Custodial Parent - The parent with both legal custody (joint or sole) and primary physical placement of a child receiving support. The child lives with this parent most of the time.

http://www.state.de.us/dhss/dcse/got.html

Custodial Parent: A parent that has the legal right to the physical custody of its child, either under the provisions of a state law granting custody, or under the provisions of a court order granting custody of the child to one of its parents in preference over the other parent.

http://glossary.adoption.com/custodial-parent.html
The noncustodial parent is the person who does not have primary care, custody or control of the child and has an obligation to pay child support. Following is information for noncustodial parents.

http://www.state.sd.us/social/CSE/Noncustodial/

In many cases court strategies and delays are used by one parent to deliberately prevent the children from seeing the other parent and to force the other parent into financial hardship. Often a custodial or primary-care parent will use their advantage as the primary parent to alienate the children from the other parent to destroy the relationship between the children and the other parent.

http://www.glen-net.ca/ex-fathers/sharpare.html


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Note added at 42 mins (2004-03-11 04:15:36 GMT)
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What is the difference between sole custody and joint custody?
There are three aspects to custody — who is the primary care giver and has the primary residence of the child, who makes decisions about the child, and who has the right to information regarding the child. In a sole custody situation one parent is all three though the non- custodial parent should be given the right to information. In joint custody both parents make the decisions relating to the child’s health, education, religion and extra-curricular activities and both have a right to information regarding health and education. Joint custody does not necessarily mean that a child spends an equal amount of time at each residence. It is very common to have a joint custody arrangement with one parent having the primary residence. Unless the parties agree the court does not usually force by order a joint custody arrangement on the parents though it can and sometimes does so.

http://www.thepascoedifference.com/custody.html