Hi, I want to get my brother into this server and he currently has a Offical ffxi subscription and i have a few questions

1. I was wondering if he could go back and forth between the offical ffxi and Nasomi's ffxi. (I want to know so i could warn him before installing)
* Yes, you can play on both. Ashita launcher have private server profiles (Nasomi) and Retail launch buttons.

2. when i go to click on the "If you already have FFXI and ALL expansions you can download these only" links it says "failed- virus detected" and i couldn't open it. is this normal? this didn't happen to the original download
* Turn off antivirus. Some antivirus programs (mine included, Avast) thinks Ashita is a virus. Just make exception in Virus program.

3. could i just download the base download even if he has original game and all the expansions?
* not 100% sure what ur saying. The game ur downloading from here = retail some time back. And after installed you need to update the game , so then it becomes the same as retail.
I would just use the I have already installed, and follow instructions From Step 9 http://nasomi.com/instruction.php

sorry if these questions are a obvious, just want to be safe before he downloads it.