If you would like to use the WordPress Media Uploader to enable users to upload images into your WordPress plugin or theme, this is discussed in a few places online:

• Using the WordPress Uploader in Your Plugin or Theme – webmaster-source.com
• Using WordPress’ Built-in Media Upload – lewayotte.com
• Add Media Uploader to WordPress plugin – imagewize.net

In addition,

• Dimas Begunoff has developed a MetaBox PHP class for doing all sorts of things
• And he discusses how to integrate the WordPress Media Upload Box here.