I fixed the problem by unmaximising the Sketchup window and then changing the dimensions of the unmaximised window to be the same as the maximised. Makes the start up slicker and faster.
The relevant registry entry seems to be:
REGEDIT4
[HKEY_CURRENT_USER\Software\Google\SketchUp7\MainFrame]
"FirstTime"=dword;00000000
"wp.bottom"=dword;00000307
"wp.flags"=dword;00000000
"wp.left"=dword;00000000
"wp.ptMaxPosition.x"=dword;00000000
"wp.ptMaxPosition.y"=dword;00000017
"wp.ptMinPosition.x"=dword;ffffffff
"wp.ptMinPosition.y"=dword;ffffffff
"wp.right"=dword;00000500
"wp.showCmd"=dword;00000001
"wp.top"=dword;00000017
Thanks for your help.