Welcome to Librarium Online!
You can use it with the FAQ on internet on GW-site. A 5.ed version of the SW-codex is hopefully arriving within 2009.
An updated SW dex is in the works.
But yeah, find the FAQ at that link. Basically you get to use the new vehicles in the new SM dex. Some of the wargear in the SW dex is now obsolete (Fang of Morkai). All shared weapons use the new rules (assault cannons, meltaguns, etc...) while using the rules for SW specfic weapons such as Frost Blades. Use the new vehicle prices in the SM codex. The exceptions are you need to use Ven. Dreds and Rhino prices from the SW dex.