Warning: Please include a link to the DD script in question in your post. See this thread for the proper posting format when asking a question.
It's running fine for me in IE8. Note that there is a script error on that page (not related to Simple Gallery itself) that may be halting the execution of the rest of your scripts as a result in IE7. The error is:
Webpage error details
User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; GTB6; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
Timestamp: Wed, 10 Jun 2009 05:54:31 UTC
Message: 'className' is null or not an object