If there are drivers available they would be on the UMAX support site. I checked there and that model is not shown for the US and Canada support site but may be shown by selecting your country in the "Worldwide Support" list at the right of the following screen: http://www.umax.com/support/index.jsp
Based on previous discussions on this forum regarding that scanner, UMAX may not be supporting a way to use it with Windows 7: http://answers.microsoft.com/en-us/Search/Search?SearchTerm=Umax+Astra+5600&CurrentScope.ForumName=&CurrentScope.Filter=&askingquestion=false