Installing HDD on Firebox x750e

[MacUsers]

Hi there,

I'm considering putting a HDD (IDE??) in my WatchGuard x750e. Looks like, only 2.5" disk will fit, which I already have one. Can anyone tell me what other things I need to make that happen. I found a few post-installation post, but nothing that much like a How-To, if I haven't massively missed. Dose any one know any pointer? Best!