I bought my daughter a potty at about 18 months... I wouldnt do it on christams..-- make a big deal about the potty some other day.. so the potty doesnt get lost in all of the other toys that she gets taht day.
I have a graco 3 piece potty.. it has a stand alone base.. a bowl that you have to empty and a soft ring seat. The stand alone potty has a lid so you can use the potty as a step and the ring will fit on the big toilet.
It works pretty well.
I also bought a baby bjorn little potty for our second bathroom. the bathroom is small so the potty had to be really small.
I also have a folding travel potty ring that is in my diaper bag. Those big public bathrooms are pretty big and scary.
I think it is easier to start with the child on a little potty - they can put themself on and off and their feet are on the floor.
OUr daughter also started telling us "poo poo" at about 18 months... we talked about it...If I caught her in the act I would tell her she was pooping.. etc... lots of talk no training.
She trained for poop first.. at 26 months... I put her on the potty a couple of times with clothes on when she was pooping -- she cooperated.. then I took off clothes.. I knew she "got it" when I found her sitting on her potty with her clohtes on with a dirty diaper. Then I had to teach her to tell me that she had to go.. It really was pretty easy.
She trained for pee at 28 months.. I just put her in cotton panties and the first time she peed and it ran down her leg -- she was trained..
Pullups are a waste of money.