Making network analysis

Hi, I'd like to make network analysis, because we've got a very bad transfert rate between an x220 IBM series and a vms SYSTEM. Yes they are already running :) How can I checks what's going on the network. Note that I have no idea concerning the connection between my LiNUX box and the vms one. I've already check that my interface is using the e100 driver revision 1.6.29 found on intel Web site. It's configured with 100 Mbps half duplex. The transfert rate is about 10Kbytes/sec. Tranfering data with my linux sender box trought a 2Mbit connection is OK. I've got transfert rate of 200Kbytes/sec. Thanks for your help.