Well at a quick glance, I would say you might be short on RAM. On the system requirements:
Mac computer with an Intel, PowerPC G5, or PowerPC G4 (500MHz or faster) processor
512MB of RAM; 1GB recommended
Mac OS X v10.4.10 or later
1GB of available disk space
32MB of video memory
QuickTime 7.2 or later
iLife ‘08 recommended
CD drive required for installation
They do say 512MB for RAM but you can rest assured it’s much better to go with the recommended number instead and that, 1GB, would be a minimum, IMO.
With Keynote NOT running, you might try dragging to the trash the Keynote pref file (it should be here:
Macintosh HD -> Users -> Your user account -> Library -> Preferences) and look for a file named some thing like com.apple.keynote.plist. I can’t test it for you because I don’t have iWork installed at present.
Don’t empty the trash right away, launch the app and see if it’s more stable.
But just the fact that you’re a bit short on RAM, that might be the problem right there.
When did it start acting this way? Has it always been crashing since installation?