If you want to use Netflow with the 3750X models, you also need the 3Kx module. read the article here about the module and a configuration example: 3KX NetFlow Configuration : Catalyst 3750X NetFlow Support - NetFlow & sFlow Network Monitoring - Systrax
hope that helps
You can setup a windows or Linux machine with Nprobe on it. I use Windows. You would span the port you want to monitor to another port that you plugin your nProbe machine and have the nprobe machine send the traffic to your Orion system. it is a quick easy way to monitor individual ports that don't have native netflow capability just make sure you have 2 GB NICs in your machine. I do have this running with one 100mb nic and one 1gb nic adnd it works fine.
Chris.Lapoint posted a good article in the solar winds product blog. I use this setup for all of my closets that have the 3750 switches.