When you attempt to do a fresh (new) install of Exchange Server, Exchange Setup searches for installed components?

You can prevent this by using Regedt32 to navigate to:

HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\Setup

In the right hand pane, you will see Value Names and data values that approximate:

<b>AdminDest: REG_SZ : C:\EXCHSRVR\BIN
MSMailConnector: REG_SZ : C:\EXCHSRVR
Internet: REG_SZ : C:\EXCHSRVR
Services: REG_SZ : C:\EXCHSRVR
X400: REG_SZ : C:\EXCHSRVR</b>
If Exhange Server is running, Use Control Panel / Services to Stop the Exchange services. Delete the Exchange folder (defaults as C:\EXCHSRVR), and delete the Setup key.