Help! I cannot perform a Software Update!

I had to buy my Macbook for school, and have had it since 2009. When i left that school at the end of 2010 i had to hand it to the school tech team so they could re-image it. But my laptop was having troubles already by then, and i didn't have a functional DVD drive so they couldn't wipe the laptop properly and i have no idea what they did to it. I haven't been able to perform a Software Update since and am still currently on Mac OS X Version 10.5.8.

When i try to perform a Software Update, the loading bar only loads about a quarter, then stops. I then get a message saying: 'A networking error has occurred: timed out (-1001). Make sure you can connect to the Internet, then try again. Software Update can't check for updates because of a network problem.'
I have tried doing this both with a wired and a wireless connection, but still get the same result.

I have no idea what to do, and am desperately in need of an update because i need the new iTunes to be able to connect my iPhone 4 to it and sync my music.