Two suggestions, assuming you have very few such tapes to copy.
1. Find a video copy shop to do it for you, and pay them per tape or per hour to do the work, then get the digital files from them.
2. I have a Sony Digital 8 (tape) video camera. It has a neat feature - you can play back an analog 8mm video on it no problem. The good part is, the camera has a Firewire port (Sony calls it their own name, iLink) and an always-on analog-to-digital tanslator chip. So when you play a digital OR analog video tape on it, you can connect the Firewire port to your computer and capture the whole thing! It even works backwards - you can send a digital video signal from computer to camera via Firewire and record it there (digital recoding only), or just keep on passing it through out the analog video/audio cable from the camera to an external analog VCR. The camera becomes the analog/digital interface device either way. Several Sony cameras had this feature, but not all. See if you can borrow or rent one - check the manual carefully to ensure it has this feature. Or, if you have many tapes to work with, you could even buy one. I got a used one from eBay for about $200. Model DCR-TRV460, I believe.