Yes, stay with the G.Skill.
Dual channel means the motherboard can access two banks of RAM at the same time, treating it as a single unit. this allows it to move data much faster. be sure you put the sticks in the same slots as the original set of 2x2GB sticks were in.
Are you sure it is a 530, and not a 530a or a 530c? According to Dell, the 530 can handle a max of 4GB of RAM, while the 530 a/c can handle up to 8GB.
Documentation