I have a disk image of keepass, what do i do with it so it sits nicely on my Macbook pro?

Put it in Applications I know..
Am i supposed to mount it?
Unpack it?
Rename it?
Is there a keypass icon for it?
Where do the installed files sit?
Explanation of the installed directories so i know where my encrypted passwords sit etc..

I worked as a developer and its always the same..

I have been able to install KeePassX 0.4.0 on my iMac without any issue.
I did it using the command line.
First I checked the md5sum was correct for the KeePassX DMG downloaded file, then I used the hdiutil and cp commands to perform the actual install.

If you never did a command line install, you might read the following page to find some help (it is quite easy):
http://commandlinemac.blogspot.com/2008/12/installing-dmg-application-from-command.html

At least you will get a bit more troubleshooting info about what is going on behind the scene.

Good luck.

FYI, my machine runs the following Mac OS X version:
$ sw_vers
ProductName: Mac OS X
ProductVersion: 10.5.7
BuildVersion: 9J61
$ uname -v
Darwin Kernel Version 9.7.0 (…)

No Max you are not the only one. I just noticed the same thing.
Can’t install 0.4.0 or earlier versions to my Mac =(
I get the same error about filesystem not supported.

is it possible to sync the password i.e. to the iPhone?

@Max
try to save it to disk first, then mount it. If you directly try to mount it it´s often corrupt.