Installing the Aquazone theme on Windows XP?

I assume you are talking about a Litestep theme? Litestep is a replacement for your windows shell, which is Explorer.exe. It's not the easiest thing in the world to get used to, and if you are not confident with the inner workings of your computer then you may be better off with a shell ENHANCER, such as Desktop X, which doesn't replace your shell, but sits over the top of it. If you do want to go ahead and run Litestep, go over to http://www.litestep.net where you will find everything you need to know. There is even an installer that you can download, so you don't have to worry about editing your system.ini or anything. I have moved away from Litestep recently, finding Desktop X more interesting and easier to work with when building themes. But one of the other admins here, Jafo, swears by Litestep and knows as much about it as anyone. So if you do run it, and you have problems, Jafo will be able to help you.
Also, I often take Litestep themes and convert them to Desktop X themes. Aquazone is by "Gef" I believe, and I have converted his themes before. Maybe I should have a word with him about Aquazone. Hmmm..........

yes it is a litestep theme, but with DesktopX, it won't interfere with XP since it's going to stay on top of it?...and by the way do these themes or desktopX come with logon customized too or I would have to download that seperately too?....thanks for your help BoXXi I understand a lil better now...

LogonStudio is a seperate (free) program that you can download from https://www.stardock.com
You can download a trial version of DesktopX from there too.
There are lots of excellent DX themes to choose from, just take a look in the DX section.