Start with the Knoppix Live CD, and then Ubuntu is the easiest to install, or Debian with KDE GUI is the most common geek install, but it's pretty tricky to get working.
Antivirus and antispyware mostly don't exist, because most virus are written to target as many people as possible, so they design them to target Windows users. A firewall might still be a good idea though, although the risk will again be greatly reduced.
Other notable distibuitons are FeatherLinux (full OS in under 50mb), and BeOS is a good alternative media-based operating system - some hardware (like the Tascam MX2424 hard disk multi-track recorder) still uses this.