Hi Jayhawk:
Most (all generally available in USA) VHS playback equipment has built-in electronics to degrade or prevent the recording of commercial VHS tapes to other tapes or other media like DVD (the trade name is Macrovision). This is what makes duped tapes look dark, or cycle between high brightness to deep darkness.
The way it works is that the recording is processed with encoding that the playback hardware can see. The hardware in the VHS player then detects if what you are playing out to is a device capable of re-recording, and then degrades the quality if it sees another recording device "out there".
Some very old VHS players do not have Macrovision implemented (or at least not done well) and you can play commercial VHS on one of these machines while recording to another VHS - you'll get a non-Macrovisioned tape copy out of that. But finding an old (mid-80's RCA, for example) VHS machine without Macrovision can be hard - and you will also likely have to lose stereo sound, since many of these machines were not stereo capable. You can check out places like Goodwill or other thrift stores for older equipment that might fit the bill.
The other option that I would suggest would be the Dazzle video interface for your computer. Most are USB (some are firewire) based, so you take the device, plug one end into a USB port on your computer (most computers made in the past 5 years have USB ports as a rule), the plug the red/white/yellow "phono plugs" from your VHS player into the other end.
Fire up the recording program on the computer, and press play on the VHS player, and you're recording into your computer - creating a movie file. When that's done, press stop, and then use another program to convert the movie file to a DVD file. The Dazzles I've used have not had any Macrovision issues to deal with.
It's an act of love to go through the process, especially for a lot of tapes, but I've had good success in shrinking my VHS shelf space by converting to DVD.
Of course, no one should ever do this to undermine the copyright laws - I suggest this only so that people that own their media can convert it to a more practical format...
To be on my soapbox a little, this is easier to do on a Mac since the Dazzle makes use of basic provided software like iTunes to manage and view movie files...
