I don't have the 300D, but I do have the Nikon D70 and Capture 4 (the Nikon equivalent of RemoteCapture). Capture 4 won't let me shoot bulb shots via the software - only via the camera or the remote. I'm thinking they just didn't code it into the firmware/software. Perhaps Canon did the same thing as Nikon.
Cheers, Paul Mikulecky Lost Pencil Animation Studios Inc. http://www.lostpencil.com
"The art of character animation is to try to catch lightning in a bottle.... one volt at a time." Brad Bird
To control the shutter, you can use software such as DSLRFocus or Images Plus. These work in concert with a custom parallel port shutter release cable (one end plugs into a laptop's parallel port, the other into the 300D's remote shutter release plug).
You can make your own cable: see http://www.stek.ch/Stefano/Serial-DSLR for details. Or you can pay some one to build it for you... see http://www.hapg.org/astrocables.htm for Hap Griffin's cables.
Info about DSLR Focus is available at http://www.dsrfocus.com; info about Images Plus is available at http://www.mlunsold.com.
Seems very strange to me: the Canon IR-Remote Control is just sending IR signals and CAN control the camera in bulb. But the USB-connection cannot. Must definitely be a bug or lousy implementation.
Thanx for the soft- and hardware tips. Unfortunately the serial port is used for LX-200 connection and the parallel for the guide cam Maybe I have to look for an additional serial card, maybe USB to serial. Its a laptop...
Still have some hope, cause I got the latest version of RemoteCapture now