Windows RT tablets will be different from Windows 8 tablets that run on Intel chips. RT will not run any older Windows 7 software -- all of its software will use the new Metro interface. These tablets are clearly aimed at the same consumers who would buy an iPad instead of a desktop or laptop.
There's been some controversy over how expensive these devices will be. Analysts say that Microsoft is charging a lot of money to device makers for the operating system -- like ~$80 dollars -- and that means these devices will be WAY more expensive than similar Android tablets and maybe even higher priced than the iPad. However, Microsoft plans to include a version of Office on RT tablets and thinks people will decide that Office is worth a some extra dough.