Need to setup a wireless lan between 2 building 150m away .

Ok, let's look at a simple setup to get you started:

Building 1-> Router-> AP w/ HighGain External Antenna->
--- ->Tree-> --- ->
AP w/ HighGain External Antenna-> Router-> Building 2...

First, note the High Gain External Antenna. You will be needing 1 of them for each AP. :? Second, both of the AP's have to be in Bridge Mode. So be sure to find an AP that supports Bridge Mode.

I'm not the man with the most knowledge about Wireless in this Forum, but i hope that this might help you on the right way.

I've had good luck using Linksys wap54gpe, but they've never stayed up for long term use. You can always additionally order external antennae, but I've never needed them with these radios in a similar situation to which you describe. I think they run around 400-450 each.

While we chose those radios because PoE was a requirement for us (it was a very interesting project), there may be cheaper solutions out there as well. I know there are also a lot more expensive ones. We also have a permanent wireless bridge set up using dual band 2.4/5.4 SMCs which works very well.