I provided you a link in my first reply explaining how to install a custom rom on your phone. You did the first step, rooting, to installing a custom ROM, the link provides the rest of the steps. You will NOT be able to theme your phone simply by rooting, regardless of how you root. All rooting does is give you SU permission using a flaw in the operating system. There are multiple ways to root using different flaws in the OS, none of them being the "real" way.
To theme you must install a deodexed custom ROM, cyanogen is probably the most stable custom Froyo rom at this point. The link I provided explains the easiest and safest way to install a custom ROM. The only problem you might encounter using this method is the first install attempt failing. If this happens, click "install sprecovery" and then click install "clockwork," then try the cyanogen install again. Installing custom roms and theming is somewhat dangerous to do and can result in you not being able to boot. There is a program to fix this on windows, but its not exactly user friendly.
I prefer Bugless Beast but it hasn't been updated lately.
