Hey eddie, I use fsbuild for pre-flight also...here's how I do it...First, use the ACE utility to load the plane of your choice as you wish. Next, take the "total weight" number (at the bottom of the ACE screen) and transfer that number to the fsbuild aircraft "payload weight" input field. Next you have to find the empty weight number for your specific version of their 757. For instance, the empty weight of Captain Sim's 757-200 is 115,000, If you use other versions of the 757, you can find their "empty weight" number by loading them up and going to the FS "fuel and payload" screen and looking at the top number. Finally, put that number in the "empty weight" input field in fsbuild. By the way, the "B757-200PF w/ PW2040" is closest to the Captain Sim "empty weigh" numbers [114,000] so I use that specific 757-200 aircraft profile and just increase it by 1000lbs. You can always find the ZFW by adding the empty weight and payload weight together - both of these numbers are located within the FS "fuel and payload" menu.

Hope this helped

Bob