I am regular visitor of ms CRM forums, I found this question many times, to hide MS CRM gird button. Which cannot be implemented through supported customization. We can implement this through unsupported customization. For example we want to hide assign button on opportunity grid toolbar. So we can do this by writing script to hide this button on Homepage.aspx in “\CRM\_root” folder. You need to follow below steps
Step1: first get ID of assign button through Developer tools (IE8) or IE developer toolbar (below IE8)
Step2: Open Homepage.aspx page in visual studio or in notepad.
Step3: Search for “window.onload” function.
Step4: Paste this script there
Using same way you can hide other buttons on the Grid toolbar, you just need to get ID of the grid toolbar button.