Need samples - What is different between statement of purpose letter and cover letter?

I would like to apply for a HR Manager position and the employer is asking for statement of purpose letter. Could any of you provide me a sample of the statement of purpose letter. What is different between statement of purpose letter and cover letter.

Dear member,
Asking for "Statement of Purpose" when applied for the job of HR Manager is a little odd. The definition of statement purpose is "a Statement of Purpose is a sentence that you write, which states, in some detail, what you want to learn about in your research project."
As an HR Manager, what research will you do? Nothing!
There appears to be some over-zealous person at the top who is fond of using these fancy expressions. Nevertheless, when this fanciness overtakes the general approach, it creates a nonsensical situation. This could be one such situation.
I recommend you giving a relook while applying for the job. Generate more market information about the top boss. He may turn out to be whimsical. This is my guess.
Thanks,
Dinesh Divekar

exactly said by dinesh; asking the SOP is not a big deal but you should write about the things related to your applied company and the predicted things, so no point of adding your details in the SOP like how you can bring things to the company or how added advantage you are to the company, etc.