Click on policy catalog, then on the right hand pane expand your package- ie. virusscan enterprise 8.50. you will then see an option to export all policies- this will give you your xml file you can import into 4.5
Some things may not come over (can't remember if its access protection) so check that they match before you add your machines. remember to assign the imported policy to your tree structure so they apply.
I can say that we migrated from 3.6.1 P3 to 4.5 P1 two servers successfully