Welcome to Windows Seven Forums...
XP had a sort option called unsorted, wherin you can drag the photos in whatever order you wish. In windows 7 this unsorted option is removed and most likely be like this in future editions.
The only way you can sort in your own order is to either rename the images with numbers of your sort order. Or you could go to the image properties, (right click on first photo you want to come first in the list and select properties), go to details, select comments field and press F2 key and enter "1". For the second photo do the same with "2" and so on.
Now select an empty space on the folder and right click and select sort by. Here if you have Comments field, select that and uncheck others. If Comments field is not there, click on More and from the list of tags offered, select the Comments. Now select Ascending / Descending order as the case may be to get your required sort order. Though cumbersome for hundred of photos, this is one of the easiest method.
If you have a tag editor like MP3 tag editor, may be you can renumber the comments field very fast for bulk files.
