The OneCare issue of not being able to complete Defrag is normal, so ignore the report from OneCare. Basically, OneCare executes a timed Defrag. When time is up it moves on. This does not mean it failed, it just means that it didn't complete a full pass through all sectors of the drive within a limited time allotted. Even if it were to complete, the disk begins fragmenting fiels once again, due to the nature of the file system. This should have little to no impact on performance unless the disk was very fragmented. Note that Vista performs background defragmentation by default, so the OneCare defrag is actually redundant.
As for the blue screen for your camera, it doesn't matter that you didn't install the camera software. The driver for the camera is still installed for you to access it with the Windows Photo Gallery import process. So, it would appear that the camera driver is in conflict with something else on the PC. You should address this issue with the camera manufacturer or Windows support. It isn't a OneCare issue.
If OneCare never reports finding any threats, that is good. It means that you don't visit sites or perform other Internet/computer usage that is exposing the PC to threats. If you suspect that OneCare has missed a threat, that is a different issue. If the PC exhibit symptoms of infection, you can contact support to have it checked out. You can also use one of the free online scanners to confirm that all is well.
http://www.eset.com/onlinescan/
http://www.ewido.net/en/onlinescan/
http://onecare.live.com/site/en-us/default.htm
http://www.kaspersky.com/virusscanner
-steve
Microsoft MVP Windows Live / Windows Live OneCare Forum Moderator
