The SharePoint 2007 logs are by default found in the 12 Hive:

C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\LOGS\

I found this article here on throttling MOSS logs to pick and chose what you want. The interface in the Central Administration is not the best in terms of drop downs...would have been a lot easier if it was just all check boxes and power options to select all etc.! Maybe in the next version!

There is a SharePoint Logging Spy CodePlex project that allows you to debug in real time from multiple servers. The Unified SharePoint Log Viewer accessible from the Logging tool by Windows | ULS Log File Parser is great for opening SharePoint logs directly with some formatting.