Wireless setup help

The company I work for wants to connect the one office in town that have dsl internet to the other branch in Rural areas. I have attached a photo of the layout. http://img252.imageshack.us/img252/9770/wirelesslayout.jpg I am planning on buying RouterBoard 411A, 64MB RAM, L4 License x 2, Mikrotik R52H 350mW MiniPCI Card x 4, RouterBoard 433AH 3 port 128MB x 1, 5.1-5.8GHz 27dBi Grid Antenna x 4. That is what the Supplier told me that will work.

The problem is that i am new to Mikrotik and don’t really know how to configure it, i have read some of the wikis and how to stuff and not sure if they are the right configuration to use? http://wiki.mikrotik.com/wiki/Wireless_repeater . Not sure if this setup will work for me?

What i want to do if u look at the picture is that i want to connect the office at B that have dsl internet to a access point that goes to the repeater on C and then again down to A. Then another problem is that that point A is ±100m from the office due to LOS not sure if i can use cable or maybe a Linksys wap54g as a repeater or access point to connect to the office? And is it possible to configure the last client at A so u can connect to it via cable or wireless? And maybe using Wpa, Web that is secure so no one can access the WLAN? Don’t want to buy all the stuff and not being able to do the setup.

Thanks to anyone that can help me or give me links to anything that is helpful .

Anyone? Is this posible or not?