A couple of things. Looks like you got the install to complete. The problem is your add-pssnapin call. You are using the name of the snapin as the parameter name, not the parameter value. That's indicated by the "parameter cannot be found" error. The correct syntax is
PS> Add-PSSnapin -Name iControlSnapin
And the second issue is the get cmdlet is missing the "F5." namespace in it. I think there's some documentation I need to update but in the mean time, you can get the associated iControl cmdlets with the "Get-F5.iControlCommands" cmdlet. You can also use "Get-Command *F5*".
Take a look at the numerous tech tips and codeshare entries I've written around PowerShell to get you started.
http://devcentral.f5.com/wiki/default.aspx/iControl/PowerShell.html
Hope this helps!
-Joe