The Creative x-fi extrememusic soundcard ( http://www.creative.com/products/produc ... duct=14066
should be very good for recording purposes as it has support for ASIO low latency.
The yamaha mg/10 mixer manual http://www2.yamaha.co.jp/manual/pdf/pa/ ... G10_2E.pdf
shows that the mic inputs has XLR connectors and a preamp.
The manual recommends that you use external pre-amp between the guitar and a line-input of the mixer.
If you have acoustic guitar with built-in preamp just connect it to a line input.
If you an electric guitar you may be able to connect it to one of the XLR mic inputs, but you need a special cable with 1/4" mono jack at the "guitar end" and a XLR male connector in the "mixer end". But the risk is that the signal level from an electric guitar is to high for the small signal mic inputs of the mixer. You wont brake anything in the mixer but you will have lots of clipping of the signal.
Depending of the signal level from the guitar micÂ´s you may also be able to connect the electric guitar directly to a line input.
But the normal way to connect an electric guitar to a mixer is to use a dedicated pre-amp or another amplifing device as the V-Amp 2 etc etc.