While there is no way to do so as of yet, Apple is currently working on a feature to allow FaceTime through iChat.
FaceTime and iChat use different video networking so you cannot use both but FaceTime is available for the Mac (See links below) so it can be used instead of iChat as required.
No, It has 'Facetime'.
Apple does not make iChat for iPad. But if you have an iPad 2 or newer, you can use FaceTime which is very similar to iChat.
iChat is not an available feature on the iPod Touch. There is facetime for the new iPod Touch (fourth generation), but iChat is strictly for Mac laptops and desktops.
The webcam on a Mac is controlled by the software using it. Launch Photobooth, Facetime, iChat, iMovie or any other software that requires the camera and it will be activated.
Assuming the camera is not actually broken you can control the camera with software such as Photobooth, iMovie and iChat or FaceTime which can be found in the Applications folder (apart from FaceTime which can be downloaded from the link below).
There is no Windows version of iChat yet but if the Windows user is using an AIM account then you can connect to the Mac iChat user if they are logged into iChat via an AIM account. Otherwise iChat will not work. You can also connect both users via a free online video/chat application similar to Skype, it's a very useful free video/chat application that cross's both Windows and Macs well.
There is no age limit when using iChat. Anyone of any age is free to use it as they wish. Parents of younger children may want to ensure they know how their children are using iChat.
Yes using FaceTime. But they must have a iPhone 4 or a iPad 2
You cannot use the program iChat. However, you can use other instant messenger clients such as Pidgin to chat, even with people using iChat.
To communicate between a PC with a webcam and Macs using iChat you will need to get a free AIM name. You can then configure your AIM account to connect with iChat sessions. (See links below)
Yes you can.
iChat on her iMac.