Order Form Question

[birdlady1234]

I'm trying to program a basic order form - is there way to embed in the form the referral site the user came from without the user actually selecting what site they were previously on?

[Charles]

<input name="referral" type="hidden" value="http://www.some-site.com">

[birdlady1234]

So this code will tell me what site someone was on before they visited my that page?