I installed Ubuntu Linux 6.06 into my second hand Compaq Presario 700 this week and the outcome has been very impressive. The laptop has AMD Duron processor, probably 700 MHz speed, 20 GB hard drive, S3 Twister_K graphic card, 384 MB of memory. All devices can work properly, including the network connection and the optical mouse I am using at the moment.
The Ubuntu Linux can be downloaded here: http://www.ubuntulinux.org
It comes with a single CD, which can be used as the Live CD or installation. The impressive thing is, I had installed SuSe 10.1 to the same laptop before, but SuSe 10.1 could not be displayed properly due to some problem with the graphic card. Perhaps a new driver is needed for the S3 Twister_K video card.
Here are two snapshots of this Ubuntu Linux in my laptop: