"Your doing it wrong" or more to the point "You're asking the wrong question".
In SharePoint (2010?) world, I've never seen a case where you need a 2nd NIC on a front-end box. SharePoint is designed to scale out (more virtual machines) when you hit hardware limits (e.g. full NIC).
Assuming you have 1GB NIC's, I've never seen a SharePoint farm peak the NIC before it peaks CPU's and other resources. Maybe you should look at your design and ask "why am I wanting to do dual NIC's?". Is it performance of SharePoint? If so, have you enabled the various levels of cache in SP and IIS? Often I see WFE and SQL disks as being the speed limiter. I've never seen the "only" problem be a WFE NIC.
In order of "most often seen" SharePoint performance issues:
- Not enabling caching
- SQL disk latency high
- FWE disk latency or cpu's too high
- Lots of other random issues like "to much content on page"
- way way down on list: Network saturation
This answer assumes the "why" you ask your question is performance, but since you didn't give us that vital info, I had to guess :)