It can be a little awkward installing Debian in my Department's labs.
After obtaining a DHCP lease, you cannot establish any useful connection without first authenticating against a HTTP Basic page. However, as this page uses SSL and D-I's Wget is not linked against any SSL libraries, you are a little stuck.
To solve this (and to avoid resorting to ugly hacks), I created a udeb that prompts the user for their username and password (see screenshots above) and then authenticates using a statically-linked build of Curl. It seems to be fairly robust, and only bloats the ISO by about 200KB.
I've also preseeded a number of options suitable for DCS, such as using the local mirror and assuming UK locales and keyboard, etc. My modifications are available, along with some documentation on how to recreate my images. I have also uploaded a few images to our mirror.
D-I hacking turns out to be quite fun and relatively painless, but I'm now stuck for a useful project to use it again, and I probably don't know enough yet to tackle some of its Lenny goals either. Any ideas? Oh, if some d-i guru can explain how I can force the display of the "Choose suite" question without patching choose-mirror, that would also be excellent.