Yea, MacroVision is the analog copy protection scheme used by both VHS tapes (and maybe some later Beta) and the analog output of DVD players.
Basically, what it does is puts alternating white and black data above and below the visible picture, which isn't shown on the screen, but is still seen by the VCR. That extra info messes with the auto gain control of the VCR (or DVD recorder) and either results in a crappy copy with the picture'* brightness constantly changing, or the recording device sees that and stops the recording.
Archon is correct about the adapters. They're usually called "video stabilizers". I have one between a DVD player and VCR in my basement, because I have to use the VCR to feed the TV, and the VCR was receiving the scrambled signal from it'* video input, and sending it thru the RF output.
You can usually find them for $20-60 or so. eBay would probably yield pleanty of results.
Or, try to find some firmware hacks for your DVD recorder. I found one for my Lite-On LVW-5005x that gave me an extra record mode, as well as removing the region encoding and macrovision protection. I haven't tried recording with it from a macrovision protected tape, maybe I should do that to see what happens. But I know it doesn't output any macrovision encoded signal.