Where to start....
DV cameras recorded video in DV format. For the best quality results, you're supposed to transfer the DV over firewire, using a program like the freeware "WinDV", and then edit the DV AVI files, and finally encode to the final output MPEG-2 DVD.
Now, you can cheat. Editing will be much harder, assuming you want to do anything besides cutting off excess footage (anything you can do with scissors on film is not really "editing" in my definition, that's "splicing"). The cheat is to capture video to another format, like MPEG-2, using either a computer capture card, or a DVD recorder.
If space is a concern, hard drive space, I suggest an extra hard drive or two or three. You should never record video to the same hard drive being used by the OS (like Windows) anyway. Different physical drive, not just a different partition. And they're really not all that expensive. For example, this week, 300GB Seagate drives are on sale for $90, no rebates. That's a huge drive, and should accomodate a lot of video files, even uncompressed or lesser-compressed ones (like that of DV).
I would never, ever use MPEG-1 for video shot off a DV camera. MPEG-1 does not allow for interlace, and DV video is natively interlaced (bottom field). Your video would be full of zig-zag lines, blurriness, chroma trailing, and other nasty visual artifacts.
If you've got your heart set on capturing to the DV directly to MPEG-2 (DVD-ready format, minimal editing), I suggest a DVD recorder, skip the computer. I would suggest a JVC, Toshiba or Pioneer, and then use 1-hour mode for home-shot DV videos.
If you're convinced you still want to go the computer route, capturing video to something non-DV (again, MPEG-2), then I would suggest an ATI AIW Radeon (AGP card) or a Hauppauge PVR 250 (PCI card). The ATI AIW is for both graphics and video. The Hauppage just does video.
Matrox cards are very nice, but those are realtime (RT) NLE (non-linear editing) cards, meant for serious editing, and as such, come with a serious price tag ($1,000 or more!). I used to want such a card, but to be honest, I don't do that much advanced editing. I can use Adobe Premiere and use software non-RT filtering and effects, for the few times I seriously edit anything.
If you're still insisting on MPEG-1, and I really want to talk you out of it - it looks terrible, then you'll still need to capture in something like MPEG-2 or leave it DV, and then process the video after capture, for the best MPEG-1 quality, and least obnoxious artifacts.
I also do not understand "two captures from two cams at the same time" .... it's not possible. Computers cannot transfer or computer that much data at once, not on the same system. Merging two videos is something you'd want to do in an NLE, or a linear editing setup. I don't deal in linear setups, those are specialized pro equipment that cost a fortune, and have largely gone the way of the dodo since NLE digital tech came about.
You'll also have a problem with "system should be very stable working everyday without any problem and capture process should be able to started by anybody"... because most users are unfamiliar with proper computing AND video at the same time. Reseting computers after large tasks or even day-to-day is a big factor most folks miss. And then different videos can give different problems. If you're using the exact same DV cameras, same kind of content, etc ... then it would work. But it's pretty difficult to perfectly stabilize and video editing/capturing machine, especially when the users are not experts in either facet.