1) the event log -- application.
2)through the central administration , config the log settin, and then view the log file in .
3)chang the web.config and enable detail exception info display on page:
<customErrors mode="Off" />
<compilation batch="false" debug="true"><SafeMode MaxControls="200" CallStack="true" DirectFileDependencies="10" TotalFileDependencies="50" AllowPageLevelTrace="true">
Resource for moss :
www.CodePlex.com
Recomand Moss Book :
sharepoint Products and Technologic.
Office Sharepoint 2007.
Window Sharepoint Service 3.0.