There are various possibilities here:
Have a look at this:
xxwww.bruceclay.com/searchenginechart.pdf
No you will see that your site could have been included in the SE’s you list one of three main ways 1) a DMOZ listing 2) Google SERPS 3) Paid for inclusion in Teoma.
That’s the only logical conclusion I have.
What are they appearing as – organic serps or in a sponsored results box of some sorts?