I don't know anything about Acad Mechanical or how the mechanical symbols menu worked in 2005, but the symbols are just blocks that are saved in a folder somewhere on your machine, right? So couldn't you just create a new Tool Palette and put them all in there? This would allow you to drag and drop them into your drawings.

Here's a tutorial: http://autodesk.blogs.com/between_the_lines/2004/09/autocad_tool_pa.html

I have one "Master" file where I keep all of my most used blocks. I then copy and paste these blocks into a Tool Palette so I have easy access to them whenever I need them.

And yes, Autodesk retires it's older programs every year, which means no more support. I believe they just retired 2007 this year.