I've been working on this recently, it pretty simple if you have the correct hardware, if your switch doesn't support 802.3ad (LACP) then don't bother reading any more.
You obviously need at least 2 NICS in the MAC Server/Workstation, in Network Preferences select "NEW" give the connection a name and then select "Aggregation" from the drop down menu. Select the NICS you want to team up and then setup the IP configuration as required.
The next part is a little more complex depending on your switch. You are looking to do one of the following with the ports that your NICS you have teamed are connected to on your switch:
Grouping, EtherChannel, Partner...
These are the various namings for this I've com across...
Hope this helps.