Cool, I messed with it a little last night and found that it just needed "client=pub-" to return results. I use the api for mine but I use normal google for site searches. Using /custom? will use less resources than /search? . I also found that you can use &num=X to control the number of results. Have a look : http://www.google.com/custom?hl=en&client=pub-&q=test&num=1
I'll probably use /custom search with &num , the next time I have to use google for a site search :)