I think you can do it with a Feature. I'll look into that... but the following also works and sometimes can work where a Feature will not.

The following “hack” is:
- quick
- easy
- requires access to the web servers
- not a form of security
- and is not best practice! (the next service pack could replace the create.aspx page)

Note: this example hides "Wiki", "Survey" and "Sites and Workspaces". Edit the line with "Wiki|Survey|Sites and Workspaces" to what you want to hide.

Steps:

Go to your web server and to C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\LAYOUTS
Open create.aspx in your favoriate text / page editor. (I used Notepad) BACKUP THIS FILE BEFORE EDITING!
Scroll to the end and past the following JavaScript just before the "</asp:Content>" tag.

<script type="text/javascript" language="javascript"> 
  var x = document.getElementsByTagName("TABLE") // find all of the TABLEs on the page   
  var i=0; 
  for (i=0;i<x.length;i++) 
  { 
    if (x[i].className=="ms-itemstatic") //find the TDs styled for lists 
    { 
      if (x[i].innerHTML.match('Wiki|Survey|Sites and Workspaces')!=null)  // find the items to hide. 
      { 
        x[i].style.display='none' 
      } 
    } 
  } 
</script>


If you like to limit this to just for MySites then wrap the above in:

if (document.location.href.match('/personal/')!=null)    //do this just for the mysites 
{   

}