An user suggested to try the firefox extension "download them all". I never tried it, so I have no idea if it is good.
Another suggestion was Download Studio, but too bad is not free
Actually, most download manager I found around the net are not free and all the free ones I checked apparently doesn't support vista 64-bit
Give a try to Free Download Manager. Some users in their forums claims that it run smoothly under Vista 64, and it's free (it can also run in portable mode)