If you're still into your DS, games like Mario Kart and Animal Crossing work O.K. with the Nintendo Wi-Fi USB Adapter. If you have $40 that you're willing to part with to try-er out, it might be worth it. I got a fair bit of play out of mine with my friend, and it's still useful if you upgrade to DSL someday.
Also, setting up your Wii on the internet with dial-up is possible with the same piece of equipment. However, to upgrade your console to the latest version to use the Wii Shop Channel, the download could take like 10 hours, and if your dial-up connection blips out or disconnects for even a second... you gotta start all over again. NES Games only take like a few hours to download though.
Basically, it's O.K if you're away from your house or sleeping when you start planning to do this stuff, nobody has time to watch a load bar or Mario hit blocks for hours on end. But don't touch your computer while the DS or Wii is on the internet, your dial-up connection needs to concentrate on one thing at a time.