I agree with the rest: if it's at all possible, tell them "no, I just need to be alone." The fact that they have no gear and no experience gives you two additional alternatives: "I'd like to take you, but I don't have enough gear to outfit you both" and "This is not a beginner's trip - I'll design a great first trip to take you on when I get back."

If they insist on going, Phat's right: you tell them where you're headed and they have to do their own planning. I had a couple of very good friends that I loved backpacking with; we were incredibly compatible in style and what we enjoyed. But even though we might agree on the "bones" of the plan (so many miles on such and such trails, probably camping at point x, y, and z), the rule was that we were taking 3 solo trips together. Everybody planned for themselves, and we all felt free to leave the group and hook back up later, or just camp by themselves and hook up next morning - and frequently did.

So you don't have to give up a day of hiking, can you suggest that they either meet you somewhere on the second day of your hike, or could you start together and you stay on the trail a day past the spot they leave?