[Law]

DSL damnsmalllinux.org and slackware would be your best bet for a lightweight distro on a low end machine.

Or (this is a qoute from jakec)

Originally posted by jakec
here are some Distros for you to look at, I haven't used all of them but I'd highly recomend Austrumi, Slackware, puppy. Although I haven't used all of these distros they looked promising

feather Linux
http://featherlinux.berlios.de/

DSL
http://www.damnsmalllinux.org/

Puppy Linux
http://www.puppylinux.org/user/viewpage.php?page_id=3

Slackware
http://www.slackware.com/

Spinx Linux
http://www.ibiblio.org/spinix/

Crux Linux
http://crux.nu

DLX Linux
http://www.wu-wien.ac.at/us...

FreeSCO
http://www.freesco.info

Dettu Linux
http://hobbingen.uni-muenst...

hal91 Floppy Linux
http://jspiro.tripod.com/li...

alinux
http://www.ibiblio.org/peanut/

pocket Linux
http://www.pocket-lnx.org/

tomsrtbt
http://www.toms.net/rb/

Zip Ham
http://zipham.free.fr/

Grey cat Linux
http://home.wanadoo.nl/pete...

AlphaLinux
http://alfalinux.sourceforg...

SpyLinux
http://www.bluesine.com/Pro...

tty Linux
http://www.informatik.uni-b...

Bootable Business Card
http://open-projects.linuxc...

Small Linux
http://www.superant.com/sma...

Basic Linux
http://www.volny.cz/basicli...

ADIOS
http://dc.qut.edu.au/adios/

Austrumi
http://cyti.latgola.lv/ruun...

Zenwalk
http://www.zenwalk.org/

ThinTux
http://www.thintux.org/


EDIT:

Almost forgot Flash Linux, a Linux distro designed specifically for USB keys: http://flashlinux.org.uk/

you can find more here http://www.linuxlinks.com/Distributions/Floppy/
http://www.linuxlinks.com/Distributi...Distributions/

hope this Helps,

Jake