Hello, Lars. Welcome to FileMaker (hopefully).
There are at least a couple of solutions to integrating QuickBooks and FileMaker. There's one called FMBooks Connector (http://www.fmbooksconnector.com) from Productive Computing. Beezwax also has some connectivity options (www.beezwax.net/what/connectivity/fmp_and_qb). SolutionMakers offers something called 123Sync (http://developer.filemaker.com/solutions/detail/?item=solution.10000000546).
At least that should get you started. HTH.