Classical UI design, one that will not go out of style

We could always follow the UI designs of the Office applications but we also have a need to update our applications when MS has changed the design of their Office applications.

So I am thinking of using something like a 'classical' design where I will not have the need to follow the UI of MS.

Could you guys give some ideas or opinions regarding this matter?

Just use the standard controls in standard configurations. The controls will always take on the look and feel of the current theme.