when track one records onto track two

Let it Bleed (Sorry-had to homage the Stones)

I have been using Audobe Audition 1.5 for about 2 years, and I have always selcted the input I am gonna use from the windows mixer menu..."recording control"......I have never noticed anything but minimal bleed at worst. This seems to be related to the volume level to me. Maybe I'm just lucky?
Here is my related problem. I have the Lexicon Lambda into my system, it is a quad core Windows 7 computer, I am also using Adobe Audition 3. I cannot record vocals into track 2 without the music from track 1 recording into it as well. With the Lexicon Lambda the i/o are not the same as the Windows ones. But I need the Lambda interface for midi as well as mic and line in inputs. So how do I separate all of these things to isolate the track I want to record while still listening to the music from track 1?

Thank You for any help you may have for me!
Happy Holidays!
I have a pretty decent soundcard (Not as good as I'd like) and I get a slight quiet bleed over as well.

Is this something that only happens in cooledit or would it be different in a program say like pro tools?