I'm currently testing iSCSI with Intel Pro 1000 PT DualPort adapter. The performance is pretty well but is it possible to combine both ethernet ports to have a true 2Gbit link for the boot device? Intel documentation doesn't explain this.
What you want is multipath i/o (MPIO). There are different ways to configure this based on OS and san type and You're not giving us a lot of info to work on. Here's an article about iscsi mpio using microsoft's iscsi initiator and a Dell san. It should at least get you started.
This is also good reading on why you shouldn't use link aggregation with iscsi: