Problems upgrading from Tiger to Snow Leopard

I have purchased a family copy of Snow Leopard and when I installed it on my MacBook Pro, it said it would take 47 minutes to install, after about an hour and half it completely froze. So when I was confident that it was dead (even though the dvd kept on making a starting and stopping noise) I turned it off and started again, the same thing happened again but the process seem to progress more, but again it froze. The third time I used the disk utility and disk doctor which said everything was okay. This time it got within 7 minutes of installation.

Can anyone tell me what I'm doing wrong? Does this mean I have lost all my work and programmes? What should I do next?