Can I use my computer keyboard to play a virtual instrument with MC6T?
 
Second if not I have another piece of software that will let me record the piano as a midi file. So what I would like to know is can I
record several small midi files and then load them into MC6T and string them together to complete a full melody?

Answer to first question http://forum.cakewalk.com/fb.ashx?m=2835549 There are free ones on the 'net. Still not a good substitute for a real keyboard/controller.

You can import MIDI files into MC. Either with the import menu function, drag and drop from Windows or the media browser.

Yeah, I believe you can.... but... is it the best way?  No, not really. 

Hit a few yard sales and look for a used musical synth/keyboard that the folks are not using. Look for a midi output on it and make an offer.  Even cheap keyboards have midi in them now days.