teebo,

You will find most of the 'English' (or other language) files under includes>languages>english>modules>payment> ---
In your case (provided you installed correctly) you will find it in includes>languages>english>modules>payment>googlecheckout.php around line 25 or so... between single quotes; e.g. '- Or Use '
You can change the text to whatever you want -

But, it really does not end there. When you cannot find something, the ZEN-CART folks have done a great job of providing good tools for all of us to work with - including search tools. Just go to admin>tools>developers tool kit>Look-Up in all files>Key or Name: and PULLDOWN the area you wish to search in - and in your case it is >Pulldown>Catalog and enter what you are looking for - in your case it is - Or Use -

Be aware, you may get lots of results - what I do is print the results, because I have trouble remembering the path - and sometimes the page is very long -

Another Tip... when the search engine provides a really long list - and you are looking for a specific word or phrase - EVERY BROWSER has a built in search capability - for example, IE you just click on Edit>Find on this page> and check "Match whole word..."

or

In Firefox you can do a similar thing, but Firefox helps you by providing a 'green' search results box if you are entering something it has, or it will turn a light red if not...

Go fo it!

jund