1. WPA is much more secure than WEP (WPA2 is best but older kit won't allow its use)-WEP can be cracked relatively easily with tools downloaded from the Net. Having said that any form of encryption will deter all but a determined piggybacker. I can see 2 totally unprotected networks in my immediate area out of 5, so ..........
WPA can be cracked but its a lot more complicated, and currently not available to your average neighbourhood hacker!
2. It doesn't add much at all to " security" by disabling SSID broadcast - in fact with Vista PCs all it does is muck up your wireless connection!! There is a learned article on the M/SOFT site.