Hey my desktop has gigabit lan but my laptop only has 10/100 if i bought a usb ethernet for my laptop would that help speed up the connection some between the 2 computers? oh and i already have a gigabit switch
Maybe. If all parts support gigabit, if your drives are fast enough, if usb can handle the bandwith, if your processor is fast enough, if your driver is not bad, if the transmission protocoll can handle the speed, if ...
it could be faster but you will only know if you try it.
Im assuming that if your laptop only has 10/100 then it doesn't support USB3.
USB 2 only supports max theoretical throughput of 480 Mbit/s. No where near that speed in real world usage.
You might see a slight increase in speed. But no where near as fast as gigabit.