The incomplete folder is a default folder that stores your partially downloaded files. When files are 100% downloaded they are transfered from incomplete folder to your download folder.
Your Desktop is not a safe place to download files to. A virus could easily corrupt your user account & your desktop become a mess.
In past, the default download location was:
C:\Documents and Settings\"your account name"\Shared
To change the download location, go to LW's menu bar, Tools > Options > Saving & press Browse button & direct it to wherever you choose to have the download folder. The incomplete folder is always in tandem with the download folder, in same directory or one above.
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