A 850 MHz processor and 256 MB or RAM should be plenty to run Windows ME. Your videocard has little or nothing to do with the problem. First thing you want to do is to run Scan Disk and make sure there are no errors on your hard drive. Second, run MSCONFIG from the Start > Run command to see what programs run at startup. You might have a program that's running in the background that is taking up your computer's resources. If there are any you don't want, disable them.
A last ditch effort would be reinstalling Windows ME. Don't do it until you run out of ideas.