Get PhotoSuite from the Market.. it's great. You can keep the standard Gallery app for all the public photos, and hide the private ones. PhotoSuite enables you to display both.... password protected. enjoy
Try an app called VeryAndroid File protector. VeryAndroid File Protector is the most powerful tool for android phone and computer users to password protect their files/folders on android phones or computer. It guards your previous personal folders and files of almost all kinds, such as an important document, your favorite photos, music, movies or other files, and prevents other people viewing, alterting or deleting your documents without your permission. You dont need to worry about the security of your important data any more.