There is actually a lot involved.

Yes you can use a computer harddrive . Most people are putting in 120 gig.

But also you have to get all the info from the xbox drive to the new one. Now the problem with that is the xbox hard drive locks itself. So you can't just put it in a computer and copy it.

Some do a Hot-Swap whichinvolves hooking it up to a computer while it's on and powered by the xbox ( extremely dangerous )

The only other way is to mod-chip the xbox , put a new dashboard in and then put in the new drive and copy it.

Over-all it's not easy.