Tweaking preseed.cfg for semi-custom installs

[Richard Owlett <rowlett@cloud85.net>]

I'm new to Debian (actually ALL *nix) and am doing a series 
of test installs from DVD on a laptop dedicated to this.
The twofold purpose is to learn the ins/outs of Debian and 
decide just what I want in final installation.

I have tweaked 
http://www.debian.org/releases/squeeze/example-preseed.txt 
to meet many of my requirements.

There are three items I would like to set manually on each 
install:

1.  User name - effectively I'd be using it to remind how I 
intended to use that test variation -- there may be 3-5 installs
     present on the hard drive. My assumption is that 
commenting out
              d-i passwd/user-fullname string Debian User
     would accomplish that.

2.  Manually partition disk on each install
3.  Manually select use of Lilo or Grub as boot loader - YES 
responsibility for strange errors will be my own ;/

I have no idea on how to accomplish the last two.

TIA