Well there is a 2 part answer.
1. There is no such thing as an XP Recovery CD. You either use the XP CD or your dont.
2. You can make a DVD with both images, not a CD. As the XP CD combined with the Win7 Recovery CD will be to large for any CD.
So you can get the 2 ISO's onto a DVD like you want, but i dont know what good it will do you. As you cant boot to it nor use it.