Jumping in late here, and the switch should certainly work, but if you have an old VCR you may not need to buy one. I run my cable thru the VCR via coax, and my DVD and Wii thru the VCR via composite inputs (front and back). The VCR is connected to the TV by coax and acts as a RF modulator, leaving the composite inputs on the TV available for the Roku. This way I avoid getting up to manually switch between inputs. You didn't mention what make and model TV you have, but if it has coax and composite inputs then this setup should work.
I would avoid running the Roku through the VCR, however, because macrovision screws up the picture from Netflix, at least in my case. For some strange reason the VCR passes the DVD picture thru fine, though. I guess the picture might get messed up on the tape if I tried to record a DVD to VHS, but I digress.
Roku HD N1000 Serial #20G984014682 Software V. 3.1 Build 1167