XBMCbuntu and external players - help!

Hi

I have XBMCbuntu (Nvidia) running off a USB key on an Acer Revo 3610 (which has Win7 installed on the main HDD)

I like to run XBMCbuntu live rather than fully installing it and am looking to use an external player for video such as MPC HC

Having read up, I can see you need to find a playercorefactory file and modify it as neccessary - but when I plug the USB into my Win7 laptop, I open explorer and cant find this file? There are just 4 folders: .disk, casper, isolinux and preseed.

Any clues?
Thanks
Russell