Cannot find text in files

Hello people. I am a quite newby
I have this program. It's installation procedure with 3 cab files. These file are beeing extractet in the temp directory ( i found all the files).
The extracted files are containing:
1. Some dll's
2. Some bitmaps (used in the inst procedure)
2. One exe (it has actually another extension, but it can be dissasembled)
3 And one ASCII file with all text string that are coming in the messageboxes in the inst procedure
When i open the SETUP.exe in Olly, i cannot use breakpoints because the setup is only for unpacking the cab files. When the installation procedure starts setup is terminated and the files from the temp dir are running.
I don't know how to continue in Olly, because the instal process is already running.
When i dissasemble any file, i could not find the text string "The serial number is incorrect".
The bad thing is when i delete the BITMAPS the are no longer in the messageboxes, but when i delete the ASCII file (that's) containing all the messages (including the "The serial number is incorrect)) the message still appears!!!
I tried to run the extractet files (by copying them to another dir), no succes.
If there is someone with same expirience, please help me.
THNX