Ah, I have a better idea of what the problem is now.

When you have finished downloading a file from LimeWire, it is located in a regular Windows folder. So it isn't just available through LimeWire's Library tab. Open up Windows Explorer or My Computer and browse to, say, C:\Program Files\LimeWire\Shared. The folder where the file is saved to depends on your LimeWire settings though. If you're not sure where that folder is located, from LimeWie's top menu click "Tools" -> "Options", then select "Shared" from the tree.

Once you've opened that folder with Windows Explorer or My Computer, start MS Outlook and create a new message. Then from the folder, you simply drag the file onto that new message (select the file, hold down the left mouse button, drag to the e-mail and release the left mouse button).

You may also get some more help by posting your question in the LimeWire forum on this site.