I've sieged in Native a few times.
Step 1: Get tons of renown. Get a hundred or whatever, get a moderately sized force of Swadian Knights or Khergit veteran archers (pure mounted force), get a Heavy/Spirited Courser and a good lance, piss of Rhodoks and fuck their lords up over and over. You only need about 30 horse pros to start doing this.
Step 2: You should now have at least around 500-800 renown, depending on how many of them you messed with. Recruit a shitton of Vaegir archers or Rhodok Crossbowmen and train them up.
Step 3: Raise battle size and attack; have a few heroes with good shields to soak arrows and watch you pro archers or crossbowmen shoot everything on the battlements as you approach. Bring a polearm, a sword, a shield, and some backup Javelins or Jarids or something. The polearm should be something like a Balanced Military Scythe, a hardcore one-shot-head-splitter you can use to back up your heroes and stop your archers from being destroyed once you make it on the walls.
Step 4: Laugh. Your pro rangers will be annihilating everything they have line of sight on by this point because at raised battle size (I think this is how it works...) you should have an unreasonable number of archers on your side.
Toony: Yes it is.