Annoying Leopard Bug

It could be a problem with spaces.

Try unticking the option in the spaces pref pane 'When switching to an application, switch to a space with open windows for the application'.

 

I did have a similar problem in finder indeed.

It's a flashing from inactive to active randomly when opening a finder window.

I figured it only occurred in Icon view and Cover flow, and every "flash" was one preview being loaded (pictures and videos only).

I re-installed flip4mac and perian, however that did not solve the problem.
Also I noticed once the previews were loaded, I could re-open the finder window without the flashing happening again.

... in the end, after a while it just disappeared.

Not very useful I know sorry.
But maybe it helps in some way or at least gives you some hope

 

I had a similar problem with 10.5.3 that eventually went away on it's own. Whenever I opened a folder with lots of video files the Finder border would flash between active and inactive while the thumbnails loaded. Once they'd loaded it was fine. I already had Perian and Flip4Mac installed, the videos were different formats (mp4, avi, mov). I tried repairing permissions, zapping PRAM and running some of the scripts in Onyx but nothing fixed it.

I gave up for the evening, put my Mac to Sleep and resolved to sort it in the morning but by then the problem had disappeared. Touch wood, it hasn't come back.

 

Yes this is a weird problem. I think it might be some kind of cache the finder prepares (sort of like an index)... and maybe there is some bug in that process.

Still this does not resolve the OP's problem. Sounds like it could be some sort of expose problem also? Did you try to turn it off?