Cisco Works has the ability to match up IP address and MAC address to an Catalyst switch port, however is very expensive software.
There is a command to show which MAC address is connected to which port.
CAT5000 Command = sh cam dynamic
CAT2924 & 2950 Command = sh mac-address table
You then have the task on maching MAC address to PC, if you use DHCP then the info is on the server otherwise on the router use sh ip arp to match IP to MAC.
Cheers
Mark