lucy24 - 7:47 am on Dec 9, 2012 (gmt 0)
Urk. Please tell me that's That Other Server, not Apache. You will need someone else to do the line-by-line translation.
What on earth are all those cookies doing in the logs? (And, o/t, what's that __utmb and __utmz business? I see it all over the place when I'm cleaning up cookies in my own browser. Got a nasty feeling it's something to do with GA.)
Anyway, it's no use looking at the /thanks page, because the referer for that will always be something on your own site-- most likely a Confirm Purchase type page. You need to look at the visitor's first appearance on your site.