Jittery and slow suggests this is a resource issue.

The 1 MB of RAM is the least you should run with a PowerPoint show. Consider
further upgrading the RAM to reduce the systems need to write out memory
pages to the HD.

Reduce the size of the pictures to the appropriate level.  PowerPoint can
only display a set number of pixels.  If the pictures are saved at a higher
resolution, then PowerPoint has to manipulate those, but it still can not
project them.  Down-sampling the picture resolution will reduce the amount
of work the CPU has to do.

Make sure nothing else is running.  If possible, remove the computer from
the network and shut down the virus protection and any un-required programs.

Always try to run the show from the hard drive, not from a network/CD/DVD/or
removable drive.

Ensure the video graphics card has the latest updated drivers from the
manufacturer's website.