You could try running with gentoo (about as light and extensible as it comes).
But realiticly for hosting downloads you might be better off milking a cheap hosting account from somewhere in the WWW.
I believe ASmallOrange has some good pure bandwidth plans that will allow you to host static content (html pages) and files, that are on the inexpensive side
Firefox: no, its not the end all solution, it has its own issues and in time it will be just as insecure as IE, when its hit Firefox 6, if it makes it that far. Oh, and AOL pays for it, incase you didn't know.
Microsoft & Windows: If you hate it so much, move to linux, or bsd, or anything else, stop complaning and move on.
Good starting places:
Gentoo Novell SUSE Fedora Core Apple 
