Can I force Mac OS X to select certain Wifi network? When I turn on Wifi on my MacBook, it always selects some open network.

Can I somehow force the system to choose another network (it is password-protected but I have the password stored in the Keychain and it keeps choosing the open one)?

I'm using Mac OS X 10.7.4.
Sure. Just go to System Preferences/Network, select Wifi and click Advanced. A list with all the Wifi networks you've been connected to will appear. Just rearrange the connection order (the ones you'd like to connect first on top) by drag-dropping. 

Also, delete any unwanted network SSID (network names) if you no longer want to auto-join that.