If we have a wireless modem and connect one mac to another via networking then transfer files from one to the other does that interfere with the internet bandwidth? Can one surf the web while someone else uses the modem for transferring files?
What miles01110 means is that your local bandwidth will be being used by the file transfer. Depending on how fast your Internet connection is, whether or not your router/modem is doing any QoS, etc. you may notice a decrease in your Internet browsing speed.