Can I deny "Internet Explorer" via GPO and use Google Chrome as a default and the only Browser?

I think that you can try and use Software Restriction Policies (SRP) and deny access to "Program Files\Internet Explorer\iexplore.exe" to restrict IE. Also if you have Win2008 R2 as a DC and all of your clients have Win7, then you can use the new feature that is similar to SRP but much better and it is called AppLocker, which can also be found on the list the other Group Policy Settings:

On a Windows 7 Client go to:
Group Policy Editor ("Start", in the search field enter "gpedit.msc") -> Computer Configuration -> Windows Settings -> Security Setings -> AppLocker.

Just be adviced that if you use SRP first and then you apply some policies with the AppLocker then the AppLocker settings will take precedence and will override any settings that were defined through SRP and all of the SRP settings will be instantly disabled.

You can find more info about the new AppLocker feature on this two links:
http://technet.microsoft.com/en-us/windows/dd320283
http://technet.microsoft.com/en-us/windows/dd320283

Deny access to iexplore.exe executable with file system rights. You might have problems with other windows components and it might be easier just to educate the users. The European releases of Windows have a non-IE and a non-MediaPlayer version.