Selecting one of many wireless signals??

My neighborhood has many secure wireless networks that show up along with my own secure network whenever I boot my iMac or MacBook. Unfortunately, both my computers seem to attempt to link to networks that are not mine.

At boot time, how can I force the selection of MY network over all the others so that I don't continually have to open the Wi-Fi window and change the selected network from some stranger's to mine?

If you've never connected to these networks - it shouldn't try to join that network on its own. You can set the priority by going to Network Preferences > Advanced - then look at the wi-fi tab and drag the networks into the order of your preference.

And delete all those other networks from the Preferred Network box.