The easiest tool to install and manage Google Chrome themes is the XChrome Themes Manager. The new Beta 5 is even better. Basically you don't have to manually replace dlls or anything you just switch between themes.

New X Chrome features

* New Google Chrome themes easily installed
* One-click switching of Google Chrome themes
* Preview available Google Chrome themes and other details like theme author and version
* Single place to view and manage your Google Chrome themes
* Can create new themes through Google Chrome Theme Maker

Zip download http://elitehudson.com/XChromeP5.zip SOME HAVE REPORTED A TROJAN IN THIS FILE - PROCEED WITH CAUTION

Looks good - I probably will stick to one theme though... Is this still useful if you are going to keep the same theme for awhile?

My virus software detected a trojan in this download...

I had someone message me with that same issue. But the link is directly hosted on the authors website. That other person was using a cheap online virus checker that detected a trojan (online anti-viruses usually do even if the file is clean so they can sell you software) What anti virus are you using?

That being said, it is an external site and I cannot control what gets hosted there.

Avast! 4
It's highly recommended by many, even in stores, and has won several tests against e.g. Norman or Norton.
It has never gone wrong either...

yeah, the theme pack is a trojan. Avira found it too.

Ok, I use Avast too on my other machines. Were you able to "heal" the file? I am scared of downloading now. I put a notice beside the link.