I cannot vouch for the ebuyer brand but I understand one of the members here has a dsl modem from them and its fine, I use Linksys myself but only because it was the cheapest one at the time.
Yes use either a pcmcia wires or wireless or infact a usb key type all will do the same job though the pcmcia ones are less suseptable to getting knocked out. If all computers are close then you'll be fine they have depending on your location a range up to 200m
Still it does not harm to get it in before hand because you can get your network set up and tested.