Helper or Library?

[eluser]James Burton[/eluser]
Hi all,

I'm starting to get the hang of using CodeIgniter.
But here's the deal.

Several parts of my website will need to send email, using the email helper, but instead of typing out all the settings each time I want to create a function that I can pass the simple details (to, subject, message) to.

Should this be done using a custom helper or library? Or does it really matter?

I've tried creating a helper but I get the following error..
Using $this when not in object context

If someone could lay out the best practice of going about this it'd be a great help.

Thanks in advance!