Quickie blog post: SharePoint SDK available, quick note on discusson lists
The Sharepoint SDK (officially, the "SharePoint Server 2007 SDK: Software Development Kit and Enterprise Content Management Starter Kit") is downloadable from microsoft.com. If you develop .NET applications for SharePoint, or support said applications, then you're going to need this sooner or later. Note: it's also viewable online.
the second quick note: if you plan on developing anything for MOSS 2007 that modifies discussion list posts, you're going to need to remember: updating the 'body' property of the SPListItem object is all very well, but you may also need to update the SPListItem["TrimmedBody"] property too - this is the version of the body text which shows up in unquoted view. This came up in a recent support case
li["Body"] = helper.DoSomethingToBodyText(li["Body"].ToString());
li["TrimmedBody"] = helper.DoSomethingToBodyText(li["TrimmedBody"].ToString());
li.SystemUpdate();
A popular thing to do with these programatically is to auto-hyperlink or auto-format certain keywords in text - if you don't update both variables you end up with only the quoted view showing your changes.