I beg to differ Alucardx23.
The poster, according to the Model number WD1200BEVS has a 120 GB Sata Drive.
In answer to the original posters question…
Unless there are specific limiits imposed by the manufacture of your laptop…motherboard chipset etc (better ask them) you have a lot of options for 2,5 inch Laptop Drives. WD Blue come in sizes rangging from little ones like yours up to up to 1.0 terrabytes (that’s a big one) Any 2.5 Sata will physically fit. Look here to make a choice. http://www.wdc.com/en/products/products.aspx?id=800 Buy the largest that you can afford. Drives are pretty cheap.