I have a always on windows 7 machine
I only have one ethernet port on the bord but have a usb 2.0 to ethernet adapter
I would like to connect the usb adapter to my isp modem then use the motherboard ethernet port to connect to my main wifi router
 
how would I set this up easy?

I have a VPN service. Problem is when the service is active my other devices don't work 100 percent. 
Example streaming, instead of through the local network it goes over the internet. 
My thought is I can use the PC to allow VPN to work while still having all devices work properly. Another advantage is all my networked devices are on the VPN network. 

intertan
I only have one ethernet port on the bord but have a usb 2.0 to ethernet adapter
I would like to connect the usb adapter to my isp modem then use the motherboard ethernet port to connect to my main wifi router

There is no inherent advantage to trying this setup. You'll end up splitting your networking with two adapters on a single subnet. Unless you have a way to NIC team the interfaces you'll not encounter any benefit, only issues in routing and response. Even with NIC teaming you would need a switch that would be able to do etherchannel in order to gain any amount of bandwidth that would give any  perceivable sort of increased response.
 

intertan
I have a VPN service. Problem is when the service is active my other devices don't work 100 percent. 
Example streaming, instead of through the local network it goes over the internet. 
My thought is I can use the PC to allow VPN to work while still having all devices work properly. Another advantage is all my networked devices are on the VPN network.

 
If your VPN service is setup properly then only the work IP addressing segment would be allowed through the VPN itself. All other traffic which is not determined to be for the corporate address segment would be tunneled through your normal gateway to the internet itself. This should not interfere with any other personal connections providing the VPN is not designating all triaffic to flow through it's interface. If that is the case then you will see any traffic flow out of the virtual interface for the VPN and no traffic would be segmented outside of that connection.
 
I would talk with whomever setup the VPN connection to ensure only the traffic designated for the corporate side (if this is for a work connection) is properly configured as you don't necessarily need to have any personal traffic (music streaming or the like) to be traversing their infrastructure. Additionally opening any additional LAN connections which would bridge the two is certainly something not to do. Especially if the VPN is for any work you are doing which needs to be secured.