I would recommend going with it at a service. The problem might be more compicated than you can handle and buying parts for it until you realise which one is broken doesn't seem like a smart thing to do.
While you can purchase parts for a laptop, thier more challenging to work with than standard desktops. In addition, if you do not know about computer hardware, it may be very challanging for you to fix this on your own.
If you have important data on your drive, what you can try to do is remove the drive from the laptop and plug it into a desktop via a USB/IDE connector to see if you can access the drive.
You can remove the drive from the laptop and try to boot into the BIOS. If it still "lets the smoke out", then the system is fried, though the HD may be recoverable as far as your data is concerned. If it can get to the BIOS, then it may be the HD, but in my experience smoke is usually associated with stuff other than the HD. Save the HD, get a new laptop and a docking bay for the HD (costs about $25) and you may be able to recover your data files.
Well..the smoke comes out when there is something burning inside due to overheating. If the laptop is running fine then it is ok, otherwise you need to worry about. Better you take it to the hardware engineer.