Are you starting and need documentation about SharePoint, create custom applications and how we can start,
Microsoft have a excelent manual about Developing in Sharepoint, here a link to download:
Developing Custom Applications with SharePoint Server 2007
Every day i see SharePoint that,now and future... have been working with Sharepoint about 2006 when microsoft have launch the Sharepoint 2007 beta trials, now is such a powerfull tool, but first time i work, was very hard to get all that litle things dont have docs, but now have a lot of info and external tool, SharePoint is growing every day...
Hope this Help