Changing the time of photos

I have changed the time of some photos in Windows Gallery (using Microsoft Vista) and the times on the hard drive have not automatically changed. The original JPeg files were taken on a Canon Powershot. Has anyone any ideas how to reconcile them - the reason I wouod like to change them is that I took pictures with 2 separate camersa and when I imported them into the hard drive and then Adobe Photoship of course the sequencing is not right with the two sets of pictures. The time on the hard drive is an hour before the time in Gallery. I've tried the following

• changing the time taken in windows using the properties bar - it will change the date but not the time
• changing the time in Adobe Photoshop - usually this changes the time on the hard drive but some reason this batch will not!
• looking in the properties menu - same thing occured as the previous point

Any ideas? Thanks Katherine