iPad photos missing from folder view in Windows
You can only access photos in your camera roll via USB, I suspect you added those other albums via iTunes (as opposed to created them on you device with iOS 5). There is no official way to get those photos off your device. 


You can try to find an app that can access your photos and save them to your camera roll (e.g. Photoshop Express, free). This might be a lot a work depending on how many photos you need to copy.
You could use Dropbox to upload your photos to their servers and download them on your PC. You'll need an dropbox account, but up to 2GB is free. Dropbox allows you to select multiple photos to upload at once.
If your device is jailbroken you can get access to the filesystem and copy your phones that way.