You have a couple of choices:
1. Connect the VHS VCR's analog outputs to a DV recording device to dub the footage, then log and capture the DV footage in FCP as normal.
2. Connect the VHS VCR's analog outputs to your DV device (camcorder, VTR or converter), then connect your DV device to your Mac via Firewire. In FCP set Device Control to "Non-Controllable Device" and use Capture Now.
To achieve the best results using either method, use a TBC in-line between the VHS VCR and your DV device.
-DH