You can pick up an HP Mini-Note with a 1.2GHz processor and 120GB hard drive for just $50 more than the 1.0GHZ/4GB SSD version. But if you buy the lower end model and then later decide you want a higher capacity hard drive, it’s pretty easy to upgrade. HP Mini Note PC has step by step instructions, and a few photos showing the upgrade process.
In a nutshell, you need to remove the battery, and a few screws and lift the keyboard to access the hard drive enclosure. You can then unscrew your SSD or hard drive and replace it with another SATA hard drive.