Just a quick report... I'm currently installing WinSCP on a Windows XP system, and don't have a mouse handy.
I'm now at a dialogue box asking me whether to join "IMVU". I of course don't, but it wouldn't matter, as no combination of hitting TAB or Shift-TAB will highlight either of the two radio buttons. There's no means to access either of these controls via the keyboard.
I shouldn't have to rummage around for a mouse or have to muck around with accessibility options just to install a small utility.
Please keep this in mind when producing your installer. The software is otherwise very handy, those few times I find myself working on this operating system.