Heya Clueless!
I noticed this might be a little late as of the time of your last post, but here are a few recommendations.
For image formatting given the listed programs, I would actually size the image to the correct size in Paint, save the image as a jpeg (easier to work with IMO), and then import the image into MS Word. For specific formatting, I'd paste it in, put in 5-7 spaces, then add the next one. Make sure to put double spacing on, as it'll help give enough space to cut the cards out later. You should be able to get 8-9 cards per page this way.
Now for printing. If you have a photo printer, this would be a great way to get a good image out in high resolution. If one is not available, a regular printer would do fine (and jsut as good a job, but the image will be a bit flat). Now, what to print on:
1) Print the cards directly onto blank card stock (easily bought from Wal-Mart or Staples). While the card won't have the authentic Pokemon TCG back, it will still be able to hold up very well to being in pockets and other "abuse" that often happens to cards at parties. Once the card is in a sleeve, most players won't notice the difference so, for this option, you would probably need to buy some opaque-backed sleeves for your creations.
Option One Materials:
Plain White Card Stock
Opaque-Backed Sleeves (cheap would be fine)
Scissors (to cut cards out)
Pros: Easy, cheap, and done in seconds.
Cons: the card shape will be boxy and not authentic looking. Also, no Pokemon TCG back, so the card will always have to remain in the sleeve.
2) Print the cards onto plain white sticker paper (I think this stuff can be found at Staples, just make sure its uncut sheets and not cut into labels, name cards, etc.). The cards will print onto the sticker sheet from where you can cut and paste them onto real cards that would normally just be junk. I checked to see what type the Pikachu you spoke of would be and, since it's colorless, you would probably just want to find some old colorless Pokemon in your grandson's collection he wasn't planning on using and paste the newly printed cards on top. Just make sure the borders of both cards overlap so that there's not too much of the yellow showing. Also, when cutting the stickers out, make sure you get as close to the yellow as possible with out taking too much of the yellow off.
Option Two Materials:
Plain, White Sticker sheets (uncut)
Old, useless colorless Pokemon (Ratattas, Raticates, Pidgeys, Chatots, Starlys, etc.)
Scissors (to cut the stickers out)
Pros: Very authentic look and feel with actual back.
Cons: Time consuming with highly accurate cutting needed, stickers rub off more easily when shuffled, doesn't hold up to party "abuse" as well as card stock on its own.
My personal choice of the two is Option Two, as the sticker is great for proxying regular cards and looks very real if you don't look too close. Hope your adventure in printing CaC cards goes well!
~Cardz.