may or may not help you...
My understanding of how MacroVision works means that it's essentially the receiving device that screws things up for you. The unseen/unheard MacroVision signals cause the automatic record-gain controls on the recording VCR to get themselves in a tangle, thus causing the darkening and/or quietening artifacts.
What I'm trying to say, in a round about way, is that I'd *imagine* it's the software at the PC end that you're going to have to worry about most of all. Though it would be nice if the playback device would just drop the wanky signals.
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How many movies are you talking? And how much is the VHS2PC? Unless you've got a plethora of tapes, it may be cheaper to spring for new DVD copies. Or get a cheap VHS player while you still can -- the kids ain't gonna be kids forever, and you can shit-can/eBay the lot in 5 odd years time!
Having said all that, if you don't want to splash out on the DVDs (subject to your technical copyright infringement scruples -- I'm actually a bit fuzzy on the legality of you transferring your VHS to DVD in fact) why not just download DVD rips of the movies? It's sure to be much better quality than some shonky VHS conversion from some cranky old over-watched tape. :o)
</digression>