Hey,
I have just modded my xbox with a Xenium chip. I want to install a bigger hd and then SlaYer’s evox 2.5. I know I need to back up my original hd to my pc first. Can I do this without modifying the original hd or do I need to install evox on the hd to be able to ftp to my pc?

You'll need to mod it in some way to be able to FTP the files to your PC. You could potentially flash the X2 4978 BIOS and use the built in FTP to backup the files but this may be more trouble than it's worth.

All you have to do d/l the evox iso and burn it to cd-rw or dvd-r. Put it in your xbox dvd drive and turn it on. It should load it and allow you to setup your ip.

You can then ftp into your xbox and backup your HDD. It will not have changed anything because you booted from DVD drive.