That all depends. Some of the VHS to DVD converters you can buy are full VCR-like units. If you already own a VCR, you can buy a small box to sit between it and your computer which will mean you don't have to splash your cash on a full-size box that you don't really need for other things. This will allow you to just record the output from your existing VCR machine.
As a bonus, these boxes could also be used to record programmes from a DVR such as a TiVo or Sky+ box for archiving on your computer.