How about
Damn Small Linux (DSL)
http://damnsmalllinux.org/
DSL is a very versatile 50MB mini desktop oriented Linux distribution.
Damn Small is small enough and smart enough to do the following things:
- Boot from a business card CD as a live linux distribution (LiveCD)
- Boot from a USB pen drive
- Boot from within a host operating system (that's right,
it can run *inside* Windows)
- Run very nicely from an IDE Compact Flash drive via a method
we call "frugal install"
- Transform into a Debian OS with a traditional hard drive install
- Run light enough to power a 486DX with 16MB of Ram
- Run fully in RAM with as little as 128MB (you will be amazed at
how fast your computer can be!)
- Modularly grow -- DSL is highly extendable without the need to customize
Or
Puppy Linux
http://www.goosee.com/puppy/index.html
Mission Statement:
- Puppy will easily install to USB, Zip or hard drive media.
- Booting from CD, Puppy will load totally into RAM so that
the CD drive is then free for other purposes.
- Booting from CD, Puppy can save everything back to the CD,
no need for a hard drive.
- Booting from USB, Puppy will greatly minimise writes,
to extend the life of Flash devices indefinitely.
- Puppy will be extremely friendly for Linux newbies.
- Puppy will boot up and run extraordinarily fast.
- Puppy will have all the applications needed for daily use.
- Puppy will just work, no hassles.
- Puppy will breathe new life into old PCs
/CoMa