There is no real problem involved. The car has to meet US regulations regarding smog system (exhaust). Only modification necessary, if the car doesn´t already have it, all lights lenses have to conform to EU-regulation, meaning they have to be marked with the letter E.
The turnsignals must show orange lights and parking lights may not be orange!
In order to have it registered you need a verified copy of the US Title, Invoice to show value of car, if you do not want to accept the value Customs will decide, and invoice/receipt for Freight cost from US to Sweden.
Cost involved is 10% import duty, plus 25% VAT on the total value: Value of car + freight cost + import duty. To round it off there is some minor registration costs of Approx. USD 150,-
However, if you are moving to Sweden permantly and have owned and used the car for at least 6 months the car doesn´t have to conform to the above light regulations and you do not have to pay any Duty or VAT, only the Registration fees.
That´s basically it!
Mikael