NeatUpload is not part of mojoPortal it is a separate dll that we depend on located in the _libs folder in source code and in the /bin folder in pre-compiled releases.
To use it in a custom project you need to add a reference to the dll, you need to copy the control declaration from the mojoPortal Web.config <pages><controls> section into your feature Web.config then you can use it by studying and borrowing code from existing mojoPortal features that use it such as Shared Files, Image Gallery etc.
Hope that helps,
Joe