I love how geohots sites always stay up even though his tools don't work without really old versions of iTunes and redsn0w and 3u can both do everything his tools did while on newer versions of iTunes
If you're on iOS 3.1.2 or 3.1.3, you can use Safari on the device to go to jailbreakme.com
and jailbreak that way.
If this doesn't work for whatever reason, you can try to use SpiritNET.
If you're on iOS 3.1 or 3.1.1, you can use blackra1n, however this requires you to use an older version of iTunes. (iTunes 10 may work)
If you're on iOS 3.0, you can use purplera1n, downloadable from the Legacy Archives linked in the subreddit sidebar. This also requires you to use an older version of iTunes.
Try downloading blackra1n, plugging your iPhone in and running the software. It's one of the simplest and fastest jailbreaking tools in the history of iDevices.
By the way, if you're on Windows and you're getting the ASL.dll error, try copying "blackra1n.exe" to C:\program files (x86)\Common Files\Apple\Apple Application Support and running it from there.
No, 3.1.2 is perfect. Download blackra1n and select your OS (the Windows 7 icon or the logo) and run it. Connect your device and click “make it ra1n”. Your device will enter recovery mode and awkwardly show geohot’s face. Then you should be jailbroken and activated. You can now open the blackra1n app and install Cydia or delete blackra1n (this only deletes the blackra1n app) and you are in! Good luck!
He was pretty big in the scene way back and released a bunch of different tools. Most of the sites are still up and running, and this one (blackra1n) is like a shot of liquid nostalgia.