To my knowledge...I don't think there are any specific programs designed exclusively for making tilesets, but I could be wrong on that point; graphics aren't exactly my strong suit.
As for the other part of the question, Paint works well for minor editing, or splicing graphics, but I wouldn't recommend creating them in it. I'd go for GIMP, personally, as it's free. But if you've got some money, or know the internets well, you can go for Photoshop, as well.
Granted, there are also a slew of other graphic programs out there. Just see what works best for what you need ^^