Do you have a Snow Leopard DVD? If so then you can use it to prep the drive. You are going to need an external enclosure in order to get everything done:
How to replace or upgrade a drive in a laptop
Step One: Repair the Hard Drive and Permissions
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported then click on the Repair Permissions button. When the process is completed, then quit DU and return to the main menu. Select Restart from the Apple menu.
Step Two: Remove the old drive and install the new drive. Place the old drive in an external USB enclosure. You can buy one at OWC who is also a good vendor for drives.
Step Three: Boot from the external drive. Restart the computer and after the chime press and hold down the OPTION key until the boot manager appears. Select the icon for the external drive then click on the downward pointing arrow button.
Step Four: New Hard Drive Preparation
1. Open Disk Utility in your Utilities folder.
2. After DU loads select your new hard drive (this is the entry with the
mfgr.'s ID and size) from the left side list. Note the SMART status of
the drive in DU's status area. If it does not say "Verified" then the drive
is failing or has failed and will need replacing. Otherwise, click on the
Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from
the drop down menu to one. Set the format type to Mac OS Extended
(Journaled.) Click on the Options button, set the partition scheme to
GUID then click on the OK button. Click on the Partition button and
wait until the process has completed.
4. Select the volume you just created (this is the sub-entry under the
drive entry) from the left side list. Click on the Erase tab in the DU main
5. Set the format type to Mac OS Extended (Journaled.) Click on the
Options button, check the button for Zero Data and click on OK to
return to the Erase window.
6. Click on the Erase button. The format process can take up to several
hours depending upon the drive size.
Step Five: Clone the old drive to the new drive
1. Open Disk Utility from the Utilities folder.
2. Select the destination volume from the left side list.
3. Click on the Restore tab in the DU main window.
4. Check the box labeled Erase destination.
5. Select the destination volume from the left side list and drag it to the
Destination entry field.
6. Select the source volume from the left side list and drag it to the
Source entry field.
7. Double-check you got it right, then click on the Restore button.
Destination means the new internal drive. Source means the old external drive.
Step Six: Open the Startup Disk preferences and select the new internal volume. Click on the Restart button. You should boot from the new drive. Eject the external drive and disconnect it from the computer.