help!! Game installation errors

I'm hoping someone could offer some advise. I recently purchased 2 games (CD) from Playfirst - Diner Dash 2 and Wedding dash.
System requirements are:
* Mac OS X 10.3.9 and up to OS X 10.5
*G4 800MHz or faster, or G5 or intel processor
*50 MB available disk space

I meet all these requirements but get the following error messages when trying to install: (the come up in my library logs)

Error installing "Wedding Dash.app" to "/Applications".
Error = Creating directory at "/Applications/Wedding Dash.app" failed.
Error installing "helper" to "/Applications/Wedding Dash.app/Contents/MacOS".
Error = Could not create directory /Applications/Wedding Dash.app".
Installation finished on 2008-08-21 21:54:29 -0700

Anyone know what I can do?

thanks

First try repairing permissions with Disk Utility.
Second, are you logged in as admin?

cradom,
thanks so much for your help. I ran the disk utility and repaired my permissions - the game loaded without any errors!!!