I have had, raised and used to breed dachshunds, both Mini and Standard. What do you want to know - I can tell you anything!
First of all do some research about them. You can find the dachshund websites for dachshund rescues and usually there are regional dachshund clubs. I would have one of them recommend a reputable breeder. Don't buy from a pet store - those puppies are generally the runts, puppy mill, or imperfect puppies that breeders cannot sell on their own. Try to find a breeder that has both mother and father on site so that you can meet both parents to see their temperament. Also, check their teeth to make sure they don't have a huge overbite as this can be a dental problem in the future. Also, make sure your breeder gives you a guarantee and ask about back problems. Dachshunds that get back problems have usually been inbred. A good dachshund should not have this problem.
As far as things to expect with the breed. I prefer the standards. They are bigger than minatures, but these are still lap dogs. Standards tend to be less hyper, less barking (yappy), and and easy laid back dog. We currently have both a short hair female and a long hair male. My male is my favorite dog ever! He is a huge dachshund-42 lbs. (I got him from a German breeder). He is the sweetest, most easy going dog ever.
Short hair dachshunds hate water and cold. Which means they prefer not to go outside during rain or snow. They will, but they want right back in. Long-hair dachshunds don't care! They love snow and rain and water. They like to swim and stand in sprinklers.
Dachshunds are very loving, loyal and intelligent dogs. They do tend to be a bit stubborn and obstinent about things they don't want to do. They can be difficult to potty train in the beginning, but once they are trained they will hold it forever, because they don't want to make a mistake. I am still working with my female about jumping on the couch because she wants to sleep on it and she isn't allowed.
As with a lot of puppies, make sure you socialize them quite a bit when they are young so that they are used to a lot of different people and also kids. I have never ever had a temperament problem with my dogs, but I have seen some mean dachshunds before.
Also, dachshunds are very food driven animals so they easily respond to treats.