It's actually even easier than these guys are making it out to be
![Smiley :)](http://newforum.arcadecontrols.com/Smileys/default/smiley.gif)
Your Xenium already has a bios that accepts a larger harddrive if you are running an different dashboard (EvoX, Avalaunch, THC, etc). My guess is you probably ARE since most premodded systems will install those for you. And chances are, since you got it recently, it can accept over 137gb... double check to be sure, but you're more than likely fine on that front.
Find yourself a copy of Slayer's EvoX Auto-Installer. Its a couple hundred meg .iso that you can burn to a CD-R or DVD-R (if your xbox dvd drive doesnt like cd media). Then all you do is swap the hdd, and put in the slayer's disc. The disc will format, partition, and set up the drive for you. You can then load whatever you want to the xbox once it is initially set up. You can change dashboards if you want, if you don't want to use EvoX or whatever else you want to do.
And one more thing, you do NOT have to get a drive that is lockable. I repeat, you do NOT need a lockable drive. Locking the drive is only important if you plan to use Xbox Live, but microsoft is banning anyone with a non-stock harddrive now anyway (from what I've read) so it DOES NOT MATTER. My hard drive is not locked currently and everything works perfect.