I am assuming is what you have now in your laptop:
• 160GB (5400 RPM); Serial ATA hard disk drive
This is what you are looking at:
WD - Mainstream 500GB Internal Serial ATA Hard Drive for Laptops
When purchasing drives, what needs to be considered is the drive storage size (500GB) , drive physical dimensions (laptop hard drive), read/write speeds (up to 3Gbps. Unless you are moving large files and need it done quickly this isn't as big of a deal) and the drive connections (Serial ATA).
As you can tell, you are going up in drive size, which is fine. You are looking at replacing your existing hdd 120Gb with another hdd that belongs in a laptop, which is also okay and your connections match. This drive will work perfectly.