If you need new CDs, you can try a google search if anyone has made ISO of a set for download, just make sure you get the same version as yours. Or contact Dell and they'll send you a set, but will be at some cost.
Every Dell I have ever purchased ( and theres many) I have been able to go online and order them through customer support. XP disks used to be free of charge and they sent them to you as a one time courtesy. Now, you can order them through dell but have to pay a small fee plus shipping and handling. Just make sure you have your service tag number when speaking to customer service.
I have always dealt with the latitude and optiplex computers (business class) and the rules may vary for consumer class units, but it's still worth a try.