Yes Site import will work in a 64 bit os.
What website are you trying to import?
have you tried others? Do you have the same problem with other sites?
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.