How to programmatically determine the installed version of IE from a script
You can use WMI, I know it's not a rake script, but you could run the script (or create a .NET application) and feed the results into your application.
It's kind of a hack, but at least it will work. Here's some code from technet.
strComputer = "."
Set objWMIService = GetObject("winmgmts:\\" & strComputer & _
"\root\cimv2\Applications\MicrosoftIE")
Set colIESettings = objWMIService.ExecQuery _
("Select * from MicrosoftIE_Summary")
For Each strIESetting in colIESettings
Wscript.Echo strIESetting.Version
Next
Full Source
Once you have this information, you can pass the information to your rake script using the command line.
rake YourScript[<argument from vbscript>]
EDIT: You can copy/paste this code into a file, name it whatever.vbs, and use the cscript command to execute the script.
cscript //Nologo ie_version.vbs