Using a standard mic and an USB mixer

UPDATE:   I went and got a Blue Snowball usb mic and all is well.  I have just done a test recording the 123Echo Skype lady and me havinf a little chat.

I successfully recorded my intro and then ran into a issue as I moved to the recording exercise.

Here's my question:  Has anyone successfully use a usb mixer with a standard mic? 

My set up:

• Windows XP Laptop
• Audacity
• VAC-full version
• Skype
• Listen only headphones
• Lexicon/Alpha 2 channel USB mixer with a Sennheiser standard mic plugged in.

I followed all other instructions including purchasing and setting up VAC. My experiment has not gone well.  I was hypothesizing that since the mic plugged into the 2 channel mixer (Lexicon/Alpha) and the mixer plug into the windows xp laptop via the USB port that that might be the equivilant of a usb mic. 

 I am wondering ...before I by a XLR mic to USB preamp or a USB mic if the mixer connection is considered a "line in" rather than a mic in.  Or if this will work at all. Would apprecaite learning about the experience of anyone else who has experiemented with the use of a standard mic and usb mixer.