I am currently having cross switch issues, but did some testing between clients on the same switch and noticed very slow transfer times between clients on the same switch as well. I looked at the ports and the incoming/outgoing was very low. The ports are 10/100 set to Auto/100/full and are on the same VLAN. Checking the 5 minute average the bandwidth does not even get close to 100Mb, in fact is slowly ticks up to toward 15Mb.
Here are some numbers on file copies:
160 MB = 40 secs (should be around 10-15 secs)
2.5 GB = 3+ minutes
Any help on where to look would be appreciated.