I'm very new to panoramic photography.
I wanna create virtual tours through buildings, mainly livings rooms (also smal rooms like bathrooms).
The goal is to present them online in high quality and view them with popular devices tuch as iPad, iPhone and so on.
Welcome to the forum.
-The minimum of a Cameramodel (I've a Nikon D40 but would buy a new model if necessary)?
The 6MP D40 is the minimum, I have one. The resolution of the final stitched panorama depends on the focal length of the lens you choose; the longer the focal length the higher the resolution of the stitched pano.
The longer the focal length the more images will be required, the more difficult the pano will be to stitch and render, and the more computer power you will need.
If this is to be a commercial activity rather than hobby then in the first instance I suggest you invest in a fisheye lens - the Nikkor 10.5mm fisheye is good choice and with a D40 will provide a stitched spherical pano image of approx. 8000 x 4000 pixels - rather than new camera body (yiou can always invest in a higher res. sensor body later), and a decent pano head (plus the required software of course). An alternative lower cost fisheye would be the version of the Samyang 8mm Fisheye with the 'Nikon chip' to permit metering.http://www.dpreview.com/news/2011/11/25/samyang8nikon
I couldn't recommend your using a the standard Nikon 18-55mm 'kit' zoom lens for your proposed pano shooting application.
Interior panos are amongst the most demanding due in part to the very wide dynamic range presented by natural light through windows versus artificial interior lighting.
The D40 offers no Automatic Exposure Bracketing (AEB) functionality, but very few cameras with in-built AEB can handle such wide dynamic ranges anyway. The 'ultimate' aid for extended exposure bracketing is the Promote Control.
Will Panogear do it without problems ?
As Christian mentioned the Panogear robotic pano head is not ideal for your proposed appliction (interior spehrical panos) because the nadir 'footprint' is much larger than that of a good manual pano head. If shooting with a fisheye lens, which requires relatively few shots to provide full 360x180 degree coverage, ther is no adavanatge in usinga robotic pano head.
The Nodal Ninja range of manual pano heads are very popular and capable.
IF you choose to use a D40 on the Panogear robotic head then you will need a gentLED-TRIGGER IR shutter trigger - to allow the cemar shutter to be triggered from the Panogear mount - because the D40 doesn't support a wired remote.http://www.gentles.ltd.uk/gentled/trigger.htm
-The minimum of Computerhardware ?
It's desirable to use a computer withna 64-bit operarting system with as much RAM as you can afford; but if you stick with the D40 and a fisheye lens then in the first instance a 32-bit OS (such as Windows XP or 7/8-32bit) and 4GB RAM will suffice.
Software: -Software ?
Autopano or Autopano Pro for stitching and rendering.
Panotour Pro for creation of virtual tours that can be viewed on both Flash-enabled platforms (conventional desktops and laptops) and iDevices.
Miscellaneous: -What will be the filesize of an average Interior-Spherical Panorama to use on the Internet ?
That's a relatively meaningless question. The answer depends on the number and resolution of the sources pano images used to create the virtual tour. Panotour Pro automtically supports multi-resolution tiling enabling very large pano images to be viewed as readily as smaller images, but with more ability to zoom in to view details. This results in more files to be stored on the server, but server space and bandwidth is relatively inexpensive these days.