Works fine here with 10.5.8 although the option-clicking of the arrows works no differently than regular clicking for me. Also the month, day and year are individually highlighted for changing one-by-one by either clicking the one you want to change or pressing tab to cycle through them.
Using the Finder in 10.5.8, pressing Cmd-F to get to the Search window. I want to look for jpeg files created during December of 2008. I first specify file type = image, press the + to add another constraint, choose "creation date before" . . . today's date comes up by default, with little up/down arrows at the right to allow changes. Well, the arrows do nothing, and I can't edit the date string directly. The only change I'm able to make is when holding down the Alt key, which allows me to use the little up/down arrows to cycle through the months (but not days or years).
So, is there something I'm doing wrong? If not, any suggestions about how I can get this working?