hey, just make sure that u get an IDE drive, and any size now works with the xbox, i suggest Maxtor or Western Digital, great brands.
the main thing with upgrading the xbox HD is that some HDs can't be locked, so you won't be able to get back to the M$ dashboard or use Xbox Live! Check this site for a lockability list: http://www.lookformeb.com/hddlist/ ZipZoomFly.com has 160GB HDs for $88.49 with FREE 2nd Day Air!! http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=101005
my hdd is not locked and i can boot to my m$ dashboard. but you are definately right about xbox live.