iChat stores it's preferences and Jabber account details in two files called
com.apple.iChat.Jabber.plist in the Users Preference folder. However I am unaware of any available or easy way to script account creation using the .plist files. From what I can read from the iChat AppleScript dictionary it's not possible to add an account using AppleScript either - only work with existing accounts.
If your users used the server to authenticate to log onto the machines (or are willing to apple MCX locally):
You can manage iChat accounts via MCX, specifically the com.apple.iChat.managed preference manifest.
To manage these preferences you can do it via Workgroup Manager - click on a user, users or a group and then click the "Preferences" item in the toolbar. You can then click on the tab that says details to manage certain .plist files.
If you haven't already you'll want to add ManagedClient.app's (in
/System/Library/CoreServices) preference manifests to Workgroup Manager by click the Add button and choosing ManagedClient.app.
Double click on the
com.apple.iChat.managed item to edit it which will bring down a sheet that looks somewhat similar to Property List Viewer. Click on the disclosure triangle beside Often, and then click New Key. From the drop down for that item it provides a preset called "Account Info", choose that one. Then edit the details as necessary as you would per your setup. Note that the "%@" refers to the user's username, so you should change
I've set this up at work and unfortunately it was a bit hit or miss but a lot of it had to do with having a misconfiguration in the MCX and SSL issues.