DVIO [0] and WinDV [1] would be the closest equivalents to dvgrab on Windows. Both are super easy to use (especially the former).

For HD DV tapes there's also HDVSplit [2].

[0] https://www.videohelp.com/software/DVIO

[1] https://www.videohelp.com/software/WinDV

[2] https://www.videohelp.com/software/HDVSplit