BleepingComputer.com: Weird Network Problems

i have a small office network that i manage there are three machines Pc1 is a stock dell 3100 Pc2 is the exact same Pc3 is a 4 yr old sony vaio all have Xp home and i can only get two of the pc's to connect at a time to the internet. im using a cable modem hooked up to a router that runs 1: to trunks for a wi-fi connection 2: to a linksys switch that connects the three pc's to the internet. i can get any 2 of the 3 pc's to get on but only to at time. ive tried flushing renewing the dns ping the crap out of everything in the back room and still cant get anything to work properly. im going out of my mind

What is the make and model of the router and the model number of the switch?