The Recommended Minimum System Requirements, here, should allow even someone fairly new to installing Ubuntu or Gnu&Linux to easily install a usable system with enough room to be comfortable. A good "rule of thumb" is that machines that could run XP, Vista, Windows 7 or x86 OS X will almost always be a lot faster with Ubuntu even if they are lower-spec than described below. Simply try Ubuntu CD as a LiveCD first to check the hardware works.
Ubuntu Desktop Edition
- 2 GHz dual core processor.
- 2 GiB RAM (system memory)
- 25 GB of hard-drive space (or USB stick, memory card or external drive but see LiveCD for an alternative approach)
- VGA capable of 1024x768 screen resolution.
- Either a CD/DVD drive or a USB port for the installer media.
- Internet access is helpful.