Dear Anna,
First thing I must say is that it's "Ethernet" not "Ether" and it's "Router" not "Rooter".
Indeed you will need a wireless Router. The most likely reason you can't connect to the "old" router is that it's on a different channel to your laptop's wireless card.
You will need to buy a wireless router to match your laptop. Most recent computer's have G or B channels. I'm not exactly sure how to find out what channel you computer is. Most likely it will be included in the documentation that came with your laptop.
Router's are simple to set up, you must first set your modem into "bridge mode".
Your best bet would probably be to ring the manufacturer of your modem and ask them how to put it in bridge mode. Then ring your Router's manufacturer and ask how to set it up. Since you are inexperienced in computer's (well with routers etc) It would probably be hard for you to understand if someone walked you through it on here, would take a long time.
Sorry this probably isn't much help, wait for someone else to reply as they might know more than me.