.NET enumerations are value types, just like integers, numbers, booleans etc.
.NET enumerations are based on an underlying type, which can be Byte, SByte, Int32, UInt32, Int16, UInt16, Int64, and UInt64 (i.e. values of these types will be enumerated). When underlying type is not specified in the enum declaration, Int32(c#) or Integer (VB.NET) is used by default.
db4o stores .net enums just like regular value types like ints, floats etc. It is stored together with the containing object. It can only be loaded and stored with the containing object.