Under Linux, USB cameras use the Video4Linux interface. You need to set up a device node entry for the USB camera. Use the following command, if you have no other Video4Linux devices:
mknod /dev/video0 c 81 0 ln -s /dev/video0 /dev/video
To use the device, you need some video tools. There are a fairly wide range of tools available. http://www.thedirks.org/v4l2 has a package that is a generally named something like apps20000611.tgz, depending on the date of release. It has both X and text-mode tools. Using the text mode tools will allow you to do things like
./vctrl 320x240x24 ./vcat | rawtoppm -bgr 320 240 | xv -
There are other suitable tools available. Links to some of these tools are provided in the Linux USB web site at http://www.linux-usb.org.
This driver supports a certain chipset made by Vision, and used in a range of USB cameras (notably the Creative WebCamII). To make the CPiA camera driver work, you need to select Video For Linux (under Multimedia devices), and then select CPiA Video For Linux and CPiA USB Lowlevel Support options within the Video For Linux.
This driver supports a certain chipset made by OmniVision, and used in a range of USB cameras (notably the Creative WebCam III). To make the OV511 driver work, you need to select Video For Linux support (under Multimedia devices and USB OV511 Camera support under USB support.