Sometimes when I see these "Will it work" questions, I think of David Letterman and his "Will it Float" routines.  It is not so much will it work as it is will it work well.

My experience with B/G wireless is not good, although many on here will argue it works well.  I don't have the expertise to make my wireless work as well as I wish it would, and our local "pro" doesn't have the answer either.  I ALWAYS have good connection to the Internet, that works perfectly.  My problems are with file sharing wirelessly.  Our local Hospital has the same problem with their wireless and file sharing, my doctor finally plugged in all his notebook HP computers so he could depend on file sharing.  His theory is the steel studs in the hospital walls interfere with their wireless, I feel in my case it is some blue tooth applications I have going, or other transient waves in the same frequency spectrum. 

Wireless works for me most of the time, I only have trouble with file sharing.  If I were going to chance it working for file sharing as far as your 300 feet, I would see if it might be easier to bury a wire to the shop, or even run one overhead.