it's not a hard process.
1) first you mod the xbox. what you basically need is a USB flash drive, one of 3 games, and a USB to Xbox adapter. the flash drive is almost any drive you have lying around so that should be free. the games are like $2 at Gamestop. The USB to Xbox adapter is like $3 on eBay. there are a number of different ways to mod the xbox so the choice is yours.
2) once the xbox is modded, then you need a $3 SATA to IDE converter and a SATA hard drive. and the software i like to use because it doesn't involve a PC is chimp v2.6. what you're going to do is make a copy of the original xbox hard drive to the new hard drive. chimp will do that. chimp is a program that runs on the xbox. the remaining size of the hard drive will be newly formatted blank space that you can dump movies, games, etc. on.
now, you're going to need to power both the original IDE, DVD-ROM, and the new SATA drives simultaneously. but there are only 2 power plugs (for the original IDE and the DVD-ROM drive). so you can either buy a power splitter so that one of those power plugs is split to 2. or you can use a PC to power it. I went cheap and didn't want to spend the buck or two and used a PC. So even though you're not really using the PC, you are using its power to power the SATA drive.
3) once the old drive is copied to the new drive. you turn everything off. replace the old drive with the new drive. close up the box and voila, you have a modded xbox with over 30X the storage capacity. you can use xbmc as a media center. you can use xbmc for karaoke cd+g stuff. you can rip all xbox1 games to the hard drive very easily.
the problem with the internet is that nothing gets filtered. so i had to dig through old guides that people later told me were outdated and the method was replaced by a newer method. i jumped into xbox1 modding very late. when the 360 was about to be released. but the newer methods are far easier than the older ones. the trick is to dig through all the history to find the latest guides.
but in the end, the most expensive part of the project is the sata hard drive itself.