FileInfo.com - The File Extensions Resource

.TLB File Extension

File Type 1	OLE Type Library (Most common)
File Format	File
Common?	No
File Description	Contains user interface data for programs that support Microsoft Object Linking and Embedding (OLE); generated by Visual Basic when an OLE or ActiveX server is created and the "Remote Server Support Files" option is selected. NOTE: The file "stdole3.tlb" my contain a Trojan virus, so it should not be opened.
Program(s) that open tlb files	Windows: Referenced by OLE-compatible programs

File Type 2	VAX Text Library
File Format	File
Common?	No
File Description	Contains a text-based library of information used by a VAX / VMS system
Program(s) that open tlb files	Windows: HP OpenVMS; may be opened with a text editor

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/tlb