ds card, how would i attach the ds game card to my computer

As long as you own the original games or don't distribute any DS game card like this one, sure. I've heard you need something like a flash card to transfer roms to actual DS cards... Not sure where to look for that though.

You would need a working DS emulator (there may be some out there, I don't know of any), and something like an R4 card. As long as you follow what SHMUP said it should be mostly legal...

what if i gave three away to three of my friends

^ Don't tell anyone! ;)

LOL... look, if you're worried about it, don't do it. I do it myself, and have most of my cards backed up onto my Cyclo DS card, but I like to keep the actual cards archived back with my old NES games, just to keep things as close to ethical as possible.

If you have EZ Flash 3 in 1 with that, you can back up your save files from your DS cards using this link -> http://www009.upp.so-net.ne.jp/rudolph/nds/Backup/

it works really well. I managed to get Elite Beat Agents, Brain Age, and Phantom Hourglass onto my Cyclo DS card and I didn't have to start back over from the beginning on all of them. Really quite nice.

I highly recommend Cyclo DS with EZ Flash 3 in 1. Both of them offer a choice of white or black cards. Cyclo DS also supports the 3 in 1 card to allow rumble in DS games, as well as using it to play GBA roms. you can even load GBA roms onto the 3in1 card so it actually acts like a GBA game(you can even take it out and put it into an actual Gameboy Advance, and it will play normally)

And that's not even getting into the numerous homebrew apps out for the DS.

Oh, wait, you're asking about running these on your PC? I don't even have half a clue about that. I prefer to keep my handheld games handheld, and stylus uses. this is where I got my cyclo DS card -> CycloDS Evolution and the page for the 3 in 1 cartridges are over here -> http://www.realhotstuff.com/ez-flash-ez-v-c-58_59.html

 Most things like this are only illegal if you are turning a profit.  Gifts are usually ok :D.

no i mean on my ds wait you have to attach the game card to pc to transfer right

In one form or another, it does need to interface with the source of the roms for transfer.

Laws are murky and vary country to country.. afaik rom with legality in the US, can't distribute, even if you are just giving them away.
downloading them=illegal
24 hour rule=made up
dumping and making your own backups=illegal

as for your other question, you'll probably get a better answer on other forums which deal with roms.