with SBS 2008 this is MUCH easier then it used to be. Microsoft has migration tools that make help with the transition and provide step by step documentation:
http://technet.microsoft.com/en-us/library/sbs-2008-documentation(WS.10).aspxYou should be able to do the migration without compromising the security of your new server as long as you scan the data files you copy over with a quality Anti-Virus package on the new server.