I have a bit of experience with old analog tape - all formats - and friends who know a lot more and work in those formats daily in their profession. I have used professional and top end consumer analog video cameras and equipment for 20 years.

I'm in no way disputing the bandwidth of a dv to firewire connection but I know that every device your analog video must pass through before it reaches your hard drive can have a negative impact on image quality and you will still be starting with your old consumer vhs player and the low resolution of the vhs format.

I suggest you consider renting or ebay buying a professional quality vhs player. There is simply no comparison between consumer and professional (or at least industrial) quality decks and I believe that the playback tape deck can have a significant impact of the read of your tapes for transport and connection to your PC input.

When I converted a ton of old tapes I bought pro decks and can tell you from my personal experience that the better decks with their better heads and electronics and output made the captured files significantly of higher visual quality and image stability.

Also remember with old tapes of any format that sitting on a shelf they deteriorate and vhs was the worst possible quality of the consumer video formats so even if you chain your images through devices to achieve a firewire/dv connection to your pc you are still dealing with 220 line (or thereabouts) video and there is no such thing as up conversion in video capture.
GoodLuck