Your main account would have mac address of 11.22 and IP 22.11
Your Multiboxers will have mac address of 44.55 if they are all within the same virtual machine. Depending on the Proxy solution you use, they will either share the same IP (if you use a VPN), or they will each have a different IP (if you use commercial mmo latency reduction software - smoothping, lowerping, wtfast, etc - since only one account and therefore IP per WoW open.)
If you want each to have its own mac address, they'll all need separate virtual machines.