At Prophetic Sky, we’ve been using an in-house tool we brewed up to cope with the lack of animation playback in 2.5. We thought we’d share it with you, since I expect other 2.5 users have felt this pain! http://propheticsky.com/FlickPlayer/ Just drag the image files in question into the application window to start playing them. Space bar pauses, arrow keys moves it frame by frame, middle mouse wheel changes the playback speed. Hope it helps 
I’m pretty sure 2.5 has animation playback – you just need to set the external player in the preferences.
Looks like it’s Preferences->File->Animation Player
You could also just add your player and then it’s ctrl+f11 (or something like that).
i use virtualdub like that and its working very nice for me 