Yes, download the app from the following site (it allows you to use custom themes WITHOUT needing to patch! :) , meaning no need for taking ownership, updating the system file cache or anything like that).
Click the button that says "Play with the bits" to download the installer, and install it (no reboot required!).
Next, find a library to download custom themes. Personally, my favorite is here:
If you were doing this in XP, then installing the themes is exactly the same... just copy the theme files into
C:\Windows\Resources\Themes as you did on XP.
Enjoy the beauty!
Two of my favorite themes:
http://giannisgx89.deviantart.com/art/Sonye-Theme-for-Win7-v2-155198766 (based on the Office 2010 interface)
While you're at it, here is another great program which compliments custom themes nicely, to change your start button image: http://www.thewindowsclub.com/windows-7-start-button-changer-released . And someplace to start for new orb images: http://www.deviantart.com/#order=9&q=start+orbs .