Yes, you CAN use Enterprise Library 4.1 (http://msdn.microsoft.com/en-us/library/cc467894.aspx) in your SharePoint 2007 development projects. Here is how:
I have a webcast on this topic on MSDN China at http://msevents.microsoft.com/CUI/WebCastEventDetails.aspx?culture=en-US&EventID=1032420504&CountryCode=US. You are welcome to watch it if you happen to speak Mandarin Chinese.
Zewei Song, Ph.D.
MCPD, MCTS: .NET 3.5, MOSS AppDev, Configuration
Enterprise Services, Microsoft Corporation