Is the problem that your hardware is too slow when loading the window manager, or is it the loading of all the services and whatnot as the machine boots up?
One thing you can do is turn off all unneeded services. Open the mandrake control center and select drakXservices. You can see descriptions of each service and decide which ones to load during boot by checking/unchecking boxes. You can also try using IceWM as your graphical environment. It is much faster than KDE or Gnome and is installed by default in Mandrake 9.1 (I think). If not, you can install it from your CD. Even with these changes, boot up and shutdown will probably still be a little slower than windows, but you won't have to do it very often.
If you want to free up disk space, open the control center and select "software management". You can see descriptions of installed software and remove all the stuff you don't want.
If you want to work with a lighter OS, you can try vector linux. It is described here (with links): http://www.distrowatch.com/table.php...ibution=Vector