I had a hard time finding exactly what I needed to do in order to import a .dwp programmatically in MOSS 07. Below is some sample code:
SPLimitedWebPartManager mgr;
mgr = page.GetLimitedWebPartManager(PersonalizationScope.Shared);
XmlReader oxmlReader = new XmlTextReader(" THE PATH TO YOUR DWP FILE ");
System.Web.UI.WebControls.WebParts.WebPart oWebPart = mgr.ImportWebPart(oxmlReader, out ErrorMessage);
mgr.AddWebPart(oWebPart, "WEBPART ZONE", ZONE INDEX);
Hope that Helps.