I’m finding the always-growing resource of Adobe (nee-Macromedia) Flash-based games online as a great way to get my kids interested in, and comfortable with, getting on the computer. We recently made the switch back to Mac (I am reliving the lost days of my youth when I had a IIgs right out of college), and I’ve set up separate desktops for each boy (one with a baseball background, one with Zack & Cody). The two best sources I’ve found for kid-friendly flash games that the boys really connect with are at the Nick TV, and Disney Channel online websites. Each boy has bookmarks in Safari to the sites, and can navigate to them pretty quickly. The games themselves are pretty rudimentary, but have enough challenge, along with the built-in hook of being connected to some of their favorite TV shows, that the boys will work at them pretty hard.
On a more general note, I have to say it warms the cockles of my heart to see how many older games my boys really get into. We have a Wii at home as well, and both boys have as much fun with some of the classic titles offered through the Nintendo Virtual Console, as they do with any of the new, whiz-bang titles. Recently, they’ve been digging everything from Starfox from the N64, all the way back to Donkey Kong (Dad? Is that really Mario?).