If someone on my block has a wireless connection on their ps3 can i hack it?

May be...

If someone has an open wireless network you can easily connect and play online. The only problem is signal strength. For the internet to work well, you're going to need to be really close, or hope that they have a super good router.

If its an unsecured network, then yeah just scan and connect, if its passworded, you can try guessing it, or brute forcing it (google). Otherwise, just go buy a cheap $30 wireless router.

even if you did hack it the signal would be very weak causing problems in your online play

yea if it has no password.

lol thats evil