The HDD needs to be lockable if you want the MSdash to work, or if you want to use XBL.
Games are generally 2-3gigs, but can be as big as 6gb or as little as 0.8gb
I personaly have a 160gb HDD.
*no matter how big your HDD is you will fill it. (Murphy's law or something)
There's 3 links to lists of HDD's. It will tell you if they're "lockable"
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