It is possible to use remotes on different models.
For any Sky remote version 4 or later
Press TV
Press and hold Select and "i" on HD remotes or Select and Yellow on standard and Sky+ remotes until red led on remote flashes twice
Press 0 for standard sky, 1 for Sky+ (or 2 for sky HD only on HD remotes - but standard and Sky+ remotes will control HD boxes in Sky+ mode)
Press select - red led should flash twice
Press Sky
For any Sky remote version 4 or later
Press TV
Press and hold Select and "i" on HD remotes or Select and Yellow on standard and Sky+ remotes until red led on remote flashes twice
Press 0 for standard sky, 1 for Sky+ (or 2 for sky HD only on HD remotes - but standard and Sky+ remotes will control HD boxes in Sky+ mode)
Press select - red led should flash twice
Press Sky