Do you have a photo-editing software on your computer? If so I can throw you a few links that you could knock together to make the invite look the part.
Failing that, I'd use a printer and word:
download a "spell book"/magical looking font from dafont.com or some place like that.
Use an image from either deviant art (stock section) or google images of the spell-book you want, Make it so it looks like there is a front and back cover on each half of the paper you're using. Inside stain with tea/coffee to make it look like an aged page and have your info there.
If you like I can throw something together for you as I just realised my "guide" is a bit chaotic and confusing
I'll make it approx a4 sized and then you can downscale/add your own info without any probs
ps: it would call for some double sided printing though