Each user should have a separate log in name. Then they'll have a separate user account on the computer. Only those with admin rights on the computer will be able to see others accounts. This is the normal way of doing it. Thus, the downlds, incompletes & user preferences will all be by default in each user's own account area. eg: the default downld location is C:\Documents and Settings\"your account name"\Shared
Preferences will be C:/Documents And Settings/your_username/.limewire OR C:\Documents And Settings\your_username\Application Data\limewire

The incomplete folder is always within the same parent directory as the downld folder. Unless you split the downld folder media types or all save to the same location. Better to keep them to separate locations such as default.