API Upload file in Wordpress

I am not sure if Wordpress has API to upload file but what I am looking for is very simple:

Context: I have another plugin that I need to modify so that user can upload file in the Admin area of that plugin Solution:

1. Rewrite a new upload thru some specific path. This has nothing to do with Wordpress. I am fine doing this.

2. I prefer to use existing Media upload feature or some Wordpress upload API. I read this post but it was problematic because I want to change the text title of "Insert to Post" to "Finish Upload".

http://www.webmaster-source.com/2010/01/08/using-the-wordpress-uploader-in-your-plugin-or-theme/

Can anyone help? Prefer to go with #2 but just need to change the text. How do I change it when it is a fanbox appearing when image butto开发者_JS百科n is clicked? And the "Insert to Post" doesn't come out until the image is done uploading. The issue is how to trigger a function to change that text when fancybox is shown and image uploading completed!!?

I put Post id into url and it solves problem