Capture One Pro 4.5 will be released tomorrow (October 15). I've obtained comfirmation of the supported products for tethered operation and I know that was one of the questions that was being asked, so here it is:
Canon: 1Ds Mark III, 1D Mark III, 1D Mark II N, 1Ds Mark II, 1D Mark II,
5D, 40D, 30D, 20D, 450D/Rebel XSi, 400D/Rebel XTi, 350D/Rebel XT, 1000
Steve Hendrix
Phase One