now im ready to install my very first rom wats the best rom how do i install it
Asking "whats the best ROM" is like asking "whats your favorite color". It's all personal opinion. Some people like Sense based ROM's, some don't. Some like to overclock their CPU, some like to underclock...while some (me included) don't fool with their CPU at all. You just have to go out there and find what you like.
Start with the ROM's and MOD's HQ post in the Rooting section. The Stig (formally known as PvilleComp) does a great job of keeping it up and orgininzing. Check the screen shots of each ROM to get an idea of what it will look like after you flash it. Then get to flashing. Here's where your Nandroid will be worth it's weight in gold. After you flash a ROM, you typically have to go about restoring all your apps, all your settings and what not. If, after you've been running your custom ROM, you decide you don't like it or it's too buggy, laggy whatever, you can restore the Nandroid backup you made earlier of your previous ROM and your phone will be magically transported back in time and *poof* its like nothing ever happened. All your apps are in place, all your settings are there.
Now, if you don't know how to flash a ROM, just do a search on here...its been discussed hundreds of times and there are some really good step by step guides on how to do it. It really is very easy...if a non-computer guy like me can do it, anyone can.
And we're always here to help if you get stuck.