I see two "orbs" in the first pic (one near the doorknob, and a tiny one below and to the right of the light switch. While it's possible you captured something, it could also be caused by dust near the camera's lens.
The most convincing orb pics are ones where the orb is moving.
Keep trying though. Also, if you downsized the pics before posting them, post a full-res cropped image of the orbs if you don't mind. It might bring out some more detail.
If the activity is centered around the stairs, you could try taking pictures up or down the stairs as well.
Do you ever feel anything unusual (goosebumps, chills, or disoriented) when you hear these noises, or in any locations in the house?
EDIT: I blew up the orbs and looked closer. It looks like they are being illuminated from the right. Since the orbs are toward the left of the picture, this would lead me to think they are dust illuminated by the flash. What model camera is it? If you turn the camera around so you're looking at the front of it (such as to take a picture of yourself) and look at the camera, is the flash located to the left or the right of the lens?
[ January 19, 2005, 11:42 AM: Message edited by: Kevin P ]