I know Fluxbuntu is already in production and is at Release Candidate instead of 1.0
Both Damn Small Linux (Fluxbox) and Puppy Linux (IceWM) are excellent choices for people with low specs, but if someone wants something Ubuntu-based (with the same software repositories, release cycle, and sudo implementation) for an older computer, the only choices right now are Xubuntu, Fluxbuntu, or manual installation and configuration of IceWM (or some other window manager) manually.
If the forums' user base is any indication, Fluxbox is very popular among Ubuntu users, but there should be a significant enough number of us IceWM users to be able to put together a low-spec-friendly Ubuntu for IceWM users--IceBuntu.
I'm thinking it'd be an Alternate CD, since 64 or 128 MB of RAM may not be enough to run a live session and Ubiquity at the same time. Here's the problem: I don't know how to do it, so I'm asking the community to help out.
I've taken a look at Reconstructor, and as far as I can tell, it doesn't let you truly modify the installation the Alternate CD sets up--only add and remove packages. I wouldn't want IceBuntu to just be IceWM installed. It would be great to have some sensible configuration choices, a good default theme (ThinBlack, for example), and launcher icons for popular applications.
If you're interested in creating a IceBuntu disk or even, if it's easier, an IceBuntu metapackage, please post in this thread and let me know what you're willing to contribute and what you think IceBuntu should be like.
My technical know-how is a little weak, so I can contribute trying to coordinate people's efforts and maybe publicizing IceBuntu a bit on my Psychocats website.
Edit: It looks as if other people are much better at figuring out this ISO-remastering thing than I am. If you have torrents or other ideas you want to post up, please post them on the Ubuntu Wiki, since this thread is now becoming quite long.