Sorry but Bob is probably wrong. The connection between a Cisco router and a switch is normally a straight cable. The only one which needed a crossover cable was the old one with the builtin hub.
Your Dells would need a straight cable to talk to the switch and a crossover to talk to the router.
Could you define conflicts? What exactly is the problem? What is failing to happen? What error messages are you getting?
I assume the switch has management capabilities? Can you see what duplex/speed combinations are established? Is it showing any errors? Can you ping the management interface from the router? From the Dells?
Are you running any sort of VLAN on the switch other than the default? Any trunking? Is Spanning Tree running?
What router/IOS and is it an Ethernet or FastEthernet interface?
Can the router talk to other devices via this same switch? Can your Dells ping the router? Can they ping each other? Are your masks the same on Dells and Router? Are they in the same subnets? Are you assigning static addresses or using DHCP? Is the switch blocking broadcasts? (If this is a level three switch you may have to explicitly allow DHCP broadcasts).
Ron
#crossovercable