A colon ":" and a backslash "\" have special meaning when specifying the parameters for drawtext. So what you can do is to escape them by converting ":" to "\:" and "\" to "\\".
Also you can enclose the path to your font file in single quotes incase the path contains spaces.
So you will have
ffmpeg -i C:\Test\rec\vid_1321909320.avi -vf drawtext=fontfile='C\:\\Windows\\Fonts\\arial.ttf':text=test vid_1321909320.flv
