Hi, theres not a great deal of info around on NAS solutions that work with the xbox but ill give you my setup and hopefuly it'll help -
-Netgear Wireless Router (G)
-Linksys NSLU2 (mini linux smb file server in a tiny box, 'bout £30)
-300Gb External HDD
-2x Wirelessly connected Xbox's runnin EVOX and XBMC
Ive got my pc on the network too but that aint NAS. Ill be honest the the thing crashes a bit and it doesnt run as fast as a pc, but it does the job. If I were you, I'd return the SC101, theres no way you'll connect it to your xbox directly, you can use ur pc like you've said but that defeats the whole point of getting it and besides, it runs a custom file format so if it were to break, you'd have to buy a replacement just to get your data back. You can plug up to two HDD's into ur NSLU2 anyway.
(note- mine may just be crashing because ive got it streaming files from an NTFS hdd when it should be using an EXT3 drive)
James1987