Actually, diamond, jedi is right. TF2 is based completely in cartoon and fantasy land while INS is a real combat simulator. Nothing wrong with either, but having been a member of the TF2 division it takes a while to get used to.
Also, I would say that Dust2 is not where you should play first. Yes, it is a popular server that has a map that is easy to get used to. However, the gameplay is wholly different from what INS is intended for and it might give you the wrong feeling of what the actual game is like. Where dust2 falls short is the tactical mindset that INS was made for. If you are going to play dust2 I recommend it first for about 30 minutes to get a feel for controls, not sprinting sideways, iron sights, etc. And then play a real INS map and watch for how much teamwork there needs to be to succeed.
/rant
Have fun!