I am willing to buy an apple time capsule of 2TB, my house has 2 floors and my purpose of buying this router is that i have a good connection downstairs. So I wanted to ask you if you know about that or your personal experience with one of these routers: will the range of this router will be enough to cover my 2 floored house?
Sounds like a cop-out, but WiFi coverage is dependent on a lot of factors: type of construction, size of your estate, placement of the Time Capsule, nearby metallic objects (for example, forced-air heating ducts in the walls), other radio equipment (in particular cordless phones operating on the same frequency band), presence of other WiFi access points in the neighborhood, etc.
In general, the answer is probably yes. You'd want the Time Capsule in a central location (not in the furthest back corner of the house, not in the basement).
I have a dual-band Airport Extreme, whose WiFi radio is pretty much the same as in the TC. It's located in a central location on the 1st floor of my 2,000 sq. ft. house, and it gives me good coverage everywhere except in the farthest room over the garage.