The easiest way to manage downloads, building a history and allow to select preferences for a user is to use something like OpenID (http://openid.net/ - search on wikipedia for background infos).

OpenID is allready used by several big sites, including Yahoo (or planed to use, see flickr). It helps to make registration easier ("single digital identity") and more secure. 

OpenID is Open Source.

Ok it's aq starting point what who knows what to pacage together. When i had my items on here. I had textures for the Daz's V4.  Each different character with wildly different looks. but the textures were huge and i had single packages broken up so the downloads wouldn't take for ever to download.