Vista freezing when viewing photographs

I have an Acer Aspire laptop 120GB HDD, 512 MB DDR2 with duo processor that's
9 months old. Worked perfectly fine with Windows XP. I upgraded to Vista
Home Premium. The computer works fairly slow with Vista but the most
annoying problem is that it keeps freezing when viewing photos or video clips
in windows photo gallery. It freezes for minutes at a time. The comp also
sometimes shows a message saying "there are no videos or pictures selected"
when i am trying to flick through photos.

Any suggestions as to how to remedy the problem would be greatly
appreciated. Also , apart from debugging and defragmenting the computer, is
there anything else i can do to improve the performance and speed it up.
Windows has not recognised any problems and i regularly check for bugs etc.

Many thanks.
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DXC