Many of these sites have picture galleries with tons of pictures to download. For activities, I always suggest decorating cookies. Another activity for them is to distribute blank index cards, cut to Pok mon card size, and have the kids draw their OWN Pok mon. They can invent the names, their looks, and what special powers they have, and create an entire habitat. Then they could trade with each other.
Most kids enjoy face painting.
If you have illustrations of various Pok mon, you could let the guests pick a character to 'be'. Pin The Tail on Pikachu. Kids that find them will be able to get a gift from the prize bucket. For those gadget handy moms, get the digital camera and get some headshots of the kids. Have a cakewalk, sort of.