Ubuntu 10.04 (Lucid Lynx) 32-bit is a legacy Long Term Support (LTS) release. It was designed for older 32-bit (x86) hardware, requiring at least 256MB of RAM. 

Key Details for Ubuntu 10.04 32-bit:

• Architecture: Specifically designed for Intel/AMD x86 32-bit processors.
  
• Installation Method: Uses standard Desktop CD ISO for 32-bit, or Alternate Install CD for, low-memory, LVM, or RAID systems.

Desktop CD

The desktop CD allows you to try Ubuntu without changing your computer at all, and at your option to install it permanently later. This type of CD is what most people will want to use. You will need at least 256MiB of RAM to install from this CD.

There are two images available, each for a different type of computer:

PC (Intel x86) desktop CD

For almost all PCs. This includes most machines with Intel/AMD/etc type processors and almost all computers that run Microsoft Windows, as well as newer Apple Macintosh systems based on Intel processors. Choose this if you are at all unsure.