
When you import into Baldur's Gate II Shadows of Amn and Throne of Bhaal, don't forget to put any Pantaloons into the main character's backpack first. In case you don't know what they are, I've included the information further down this page.
To import a character from a saved game copy the whole folder containing your final save (inside Save), into the Baldur's Gate II Save folder. To import a character from a character file, export character then copy the character file (xxxxxxxx.CHR) into the Baldur's Gate II Characters folder. If your character has a custom portrait you need to copy the portrait into the Baldur's Gate II Portraits folder first. Then start a new Baldur's Gate II Shadows of Amn or Throne of Bhaal game, select the import option at the bottom of the screen & follow the instructions. You may automatically be transferred from Shadows of Amn to Throne of Bhaal whilst playing the game. If not, as far as I know, you don't need to transfer anything over; just start a Throne of Bhaal game and import your final save. Now you can continue with your adventure 
You gain the Golden Pantaloons by speaking to a nobleman in the room near the stairs, top floor of Friendly Arm Inn. Select the option "Sir, yes sir! Pantaloons pressed and ready by tonight or breakfast is free, sir!", and he will give you them and a few gold pieces.
Import your character with the Golden Pantaloons into Baldur's Gate II Shadows of Amn.
The Silver pantaloons are a little harder to gain and there is a good way and an evil way. Somewhere in the graveyard district there is a man who was buried alive. Free him and talk to the gravekeeper to discover the people who buried him are in the Bridge District. Upstairs in a house in the Bridge District, you will then find Lady Elgea tied up. The good way is to say she's in no position to demand anything and that you've not made up your mind to free her. Read the ransom note in cabinet and go to outside The Copper Coronet in the Slums at night. Get your Thief or Bard to pickpocket Welther but don't talk to him and then go back to Lady Elgea and free her. You will get less experience that way but you will get the Silver Pantaloons, which turn into something fabulous later. The evil way is to demand a ransom and read the note in the cabinet then collect the Silver Pantaloons from Welther, outside the Copper Coronet in the Slums at night. You will lose reputation but if you are evil that's a good thing.
Import your character with the Golden and Silver Pantaloons into Baldur's Gate II Throne of Bhaal
The Bronze Pantalettes take longer to get but are well-worth it. You need either 3 Stone to Flesh scrolls or 3 stone to flesh spells loaded. At some point in Throne of Bhaal expansion in Abazigal's Lair, during the quest for a scroll of reversal you will come across Iycanth the Mad. He says he will give the Scroll of Reversal if you get the eyestalk of a Beholder.
Tell him you are too good for such a small task and he will point you in the direction of three adventurers who are turned to stone. Use Stone to Flesh spells or scrolls and let the fun begin
Talk them into getting the eyestalk for you, sit back and enjoy possibly the most amusing part of the game. 
Take all three items to Amkethran. In a house via someone's roof you will find Kerrick the Smith. Get him to look in you backpack and he will turn all three items into the best armour in the game plus you will get Big Metal Rod with Frag Grenades, Scorcher Ammo and Pulse Ammo.
The big metal unit is absolutely fabulous, Grants 5% magic resistance, AC-10 and can be used with a ring or cloak of protection. Wearer then looks like a Juggernaut Golem which is excellent but has its drawbacks. I recommend you carry a spare piece of Armour otherwise you won't get round Amkethran but apart from that it is amazing! 