BlueFireZ :
Ok so i tried it myself (using both at the same time) and im using both right now, I can see that in my home sharing centre.
You can absolutely connect to a wifi and wired network at the same time. But if you open task mamager and go to the network tab (when downloading something) you will see that it is only using a single connection.
If you are on a system that has both connected, you might get better transfer rates if you disable the wireless as the system may be using it and due to a poor signal to the router may not have all the bandwidth to mak full use of your internet speed. IMHO wired is always better than wifi.
I have a laptop and I always turn the wireless off when connected by wire, this way I always get the gigabit transfer rates and no signal ssues (allows >100MB/s transfers on my local netork while wifi rarely gets over 20).