Create a simple working installer for the major OS's that includes a useful IDE, Database connectivity to least one major database and a fully functional web server. Once this is working get some people to write a standard library for date / time functions, file IO, formatting output etc.
Never underestimate how difficult it is for a new user to setup a working environment.
http://www.newartisans.com/blog/ready-lisp.html
It's Aquamacs combined with SBCL, some documentation, and some should-be-standard CL libraries. Double click and it immediately takes you into a REPL. Aquamacs recognizes most of the usual Mac key bindings, making the Emacs curve not quite so steep.
I've tried SBCL with the Eclipse plugin and it's been a huge PITA. IIRC, I couldn't get libraries to install when I finally gave up. It may have improved since, but I'm not sure. Of course the fact that many cool-sounding CL libraries had defunct websites and inaccessible CVS repos didn't exactly encourage me...
I'm just learning and my conclusion (by elimination :-)) is that for Windows the best is to use Emacs + SLIME + SBCL. There is an installation guide here: http://robert.zubek.net/blog/2008/04/09/sbcl-emacs-windows-v...
In the comments there are instructions to get ASDF working, that I haven't tried yet.
I've tried to avoid Emacs, but it seems impossible. Lisp in a Box has a lot of problems, ABLE has still too many bugs and Corman lacks GUI programming without which I can't justify the price. CUSP also has too many bugs. So I'm surrendering and looking at Emacs.
For the web server part, just use good old CGIs.