I had a desktop Sony Vaio JS VGC-JS15G with a 320GB hard disk... I tried to install Ubuntu recently in this machine but it always stuck during the installation process.. I had open disk utility and at the overall assesment it say Disk has bad sector. What should I do? Should I buy a new hard disk?
I'd say it's premature to pay for a new HD at this point. The install issues you have could depend on something else that's not related. Please try the alternative install cd, which lacks the fancy graphics and is a little harder to get started with, but works wonders. If that fails as well then you might have a real issue.
To verify if you really have hardware issues you could use http://www.ultimatebootcd.com/ or something similar. I guess your Sony came with Windows pre-installed, and that there are a lot of tools for that as well that you could use to scan your HD for bad sectors.
If you decide to buy a new drive buy a flash disk - they're more expensive but you will gain very much in performance compared to your current disk.
I'd personally not risk any valuable data on a disk that shows any signs of failure (of which a bad sector can be).
If the machine is under warranty (it's 12 months), I'd just send it back (after backing up the disk - they won't recover any data for you). If it's not, it might be worth opening it up to see if the disk itself has a longer warranty with its own manufacturer and doing that.
Otherwise just replace the disk. Small mechanical disks are cheap. Small SSDs aren't but they're superawesome.