Connect 4 computers to d-link

Question

I have 4 computers all have wireless cards 2 are older computers running win 98 - 2 are running win xp. My modem is Sympatical to go. It reads on the side of my router DWL - G700AP - on the front it reads D-Link Airplus G 2.4 GHz wireless Access. Someone had hooked it up for us 1 1/2 years ago BUT nothing works and never did except for 1 computer which is in the office of our house. The other computers are 1 upstairs and 2 others outside office all in the same house. I don't know what to do - should I have a stronger d-link router and if so what should I buy. I am not a Guru but I am ok to install software but not when it talks about cache and all the Guru stuff. I am seeking anyhelp you can offer me. thank you stardustin