Hi, Robert:
As Doug said, the 20D does not support second-curtain sync directly with studio strobes, and the same is true for all other EOS cameras as well. However, here is a popular workaround:
1. Set your studio strobe for optical slave triggering. (Some studio strobes have this feature built in. Others may require an accessory attached to the sync terminal.)
2. Mount a 580EX, 550EX or 430EX to the camera's hot shoe and set the Speedlite to its Manual mode at a low power ratio, e.g., 1/64 or 1/128. Tilt the flash head up. Set the Speedlite to second-curtain sync.
3. Set the EOS camera to its manual mode at appropriate shutter speed/aperture/ISO settings according to the desired exposure level.
4. Fire at will, within the recycling limits of your studio strobe.
Assuming a typical indoor studio set-up, this technique is pretty reliable. You may have to tweak it a bit for unusual conditions such as scrims, gobos, panels, reflectors, etc. that may block the illumination of the Speedlite from reaching the optical slave trigger of the studio strobe, but this sort of problem can usually be fixed by repositioning the power pack of the studio strobe and/or changing the position of the flash head on the Speedlite.
Hope this helps!
Best Regards,
Chuck Westfall
Director/Media & Customer Relationship
Camera Marketing Group/Canon U.S.A., Inc.