laze,
We may need you to help us a bit further here.
Why?
Well, first off, you've thrown an immediate spanner in the works by saying you've got an analogue>digital (card/box/something).
If that is the case then this should be just fine for capturing from any and all of the sources you mention ie Compact VHS/VHS, MiniDV/CAM, DVD - all of which will have analogue outputs (and probably higher-quality S-video, as well as composite video).
If that's so, then I'm struggling to know why you need or want anything else.
Typically, what these ADC devices produce is either DV (which is ideal for editing) or MPEG-2 - which can be a bit of a nuisance to edit (hard to get frame accuracy) but can save you a lot of time if there's a lot of footage and the final result is intended to be on DVD (which natively uses MPEG-2).
If you have MiniDV camcorders, decks or anything else with FireWire outputs, then the results will be better if you capture as DV via FireWire then edit and later convert to MPEG-2 or whatever the final output is intended to be.
If your computer doesn't have a FireWire port, know that PCI and CardBus FireWire cards can be bought surprisingly cheaply (well under £20 for PCI and under £30 for CarBus), so that's a no-brainer of an investment.
Do please try to look into the details rather more at your end so you can provide us with the information necessary to give you appropriate and accurate advice.
That means telling us:
* All the possible sources
* All the possible formats you might want to output as
* The functionality of your ADC device (ie what input and output sockets it has and what sort of footage it captures to)
* Good details about your computer kit, especially operating system (in detail); CPU; RAM; available free hard disk space. Graphics card details would be useful, too, as would the version of DirectX you're running if the OS is Windows.
So, do please help us to help you by letting us have this info.
Bob