My tooltips work just fine, mabey you should upgrade to the latest version? Try getting version 428 or 430. Also these newer patches have the package name that a texture is used form in the surface properties window (very helpful).
But here i will list the names of all the buttons anyway just for you guys. The list will start from left to right / top to bottom.
MODES:
Camera mode / Vertex editing
Scale mode / Rotate mode
Texture pan / Texture rotate
Change camera speed
BRUSH:
Add brush / Subtract brush
Intersect / Deintersect
Add special brush (sheets) / Add mover brush
VISIBILITY:
Show selected actors / Hide selected actors
Show all actors / Invert selection
CLIPPING MODE: (I don't know how to use these, if anybody does i would appreciate an explanation)
Clip selected brushes / Split selected brushes
Flip clipping normal / Delete clipping markers
BUILDING TOOLS:
Cube / Sheet
Cylinder / Cone
Tetrahedron (sphere) / Curved staircase
Spiral staircase / Linear Staircase
BSP based terrain
hope that helps