The most common cause of slow startup/shutdowns it antivirus software with
every possible setting switched On. Most anti-virus software will do a
quick scan of Windows just before anything loads and just before you shut
down.
If this isn't the case for you, try reducing the number of programs that
preload into your system (is tour Startup folder full of crud?). If you are
not sure what is safe to uninstall, simply *disable* suspect programs
instead running "msconfig.exe" from "Run" on the Start Menu.