This is my current situation. I live on a 10 acre farmstead in a rural area in a house at one end. my grandma lives about 300 feet to the north and my workshop/office is ~500 north of her. we both currently have dialup service and wish to upgrade to wireless microwave internet from prairieinet.net we wish to share the connection between each building. there is los from grandmas house to the shed but not from grandma to me (trees) i plan to use 802.11b wireless bridges (linksys wet11) to connect a router to a computer in the shed and media converters to use an existing thickwire landline to my house from grandmas house. will this setup work consistently and reliably or will a wireless router with cantennas be cheaper and or easier? also how do i go about setting up a barebones linux system to access the internet for the client in the shed?

I seriously doubt the Linksys will be able to reach 500 feet. Those things are notoriously under under-performers. You'll need to get a better antenna. Also it's doubtful that a normal wireless card will have the power to transmit back, even if it can get a signal, so you'll probably need a better antenna for that end too. The good news is, you're only doing point-to-point so cantennas should be fine (just point them at each other, obviously).

Your existing thicknet should work great for the wired segment. It has an effective range of 500 meters, so you're A-OK there. The bandwidth is only 10Mbit, but since it doesn't sound like you're doing much besides browsing any way, that will be fine.