If you are going to search the whole disk, you might get TOO-MANY-ROWS
as the filename is 'setup.exe' (did you expect something else?).
Depending on folder name, Universal Installer (which, as LKBrwn DBA already told you, also UNinstalls the product) can be found in such a place:
Or, choose something like this:
Start - All Programs - Oracle 10g DS - Oracle Installation Products - Universal Installer.
P.S. Oh, yes - I forgot to mention: sometimes you'll get rid of Oracle performing FORMAT C: /U, but that should be your last option.