you mean the installer can't find CFS3 or when you try to run the ETO-Game itself?
if it's the installer, direct it to the location where you installed cfs3 before. The installer is looking for cfs3 in "C:\program files\microsoft games" .
could eventually be easier to copy the whole CFS3-Folder to that position and run the installer again.
If you installed ETO to another directory or drive, you have to change a few things according the readme within the ETO-package.
Anyway, be sure to read the "readme before installation"-Guide within ETO, as its a little tricky to install. But it runs fine, when you do it step-by-step as it's described in that document.
cheers