If it's only black and white then it's easy to isolate it from the background. Actually, there are a few ways, but here's one.
1. Double-click the image in the 'Layers' palette to turn the image into a layer (this is so you can make part of it transparent).
2. Select All, then Edit > Cut to erase everything and place it on the Clipboard.
3. Press 'Q' to enter quick mask mode, Edit > Paste, press 'Q' again to exit quick mask mode, and choose Select > Inverse.
4. Change the foreground color to black, fill the selection and deselect.
As Spyderix said, PNGs will give you the best quality for importing into Flash. Keep in mind that Photoshop is predominantly a raster based application, while Flash is largely vector based. What program was the house originally created in? If it was a CAD or illustration program, you might be better off avoiding Photoshop altogether and see what export options are available to you.