If you are a newbie to Linux, you are going to have a TON of problems on your very first go. Therefore, you will need a helluva lot of community support and documentation to help you get through your teething troubles. So, for that reason ONLY, I feel a newbie should choose Ubuntu.
Otherwise, if anything goes wrong with it, Ubuntu is a bloody pain in the ass to configure. An excellent alternative is Linux Mint (*www.linuxmint.com)...its MUCH more user friendly, has a lot more functionality out of the box, and is fully compatible with all Ubuntu software.
Meri baat maan yaar, Ubuntu is gaand mein dum...I tried it like 3-4 times before I got the hang of it. WAY too much stuff to download and configure after every install...NONE of that needed with Linux Mint.
@aks_win: For your configuration, I would suggest PuppyLinux or even Damn Small Linux...the Live CD should boot fine with 192 MB as the total size of these two distros is less than 100 MB!!
If you are an advanced user, install Debian Lenny with a minimal netinstal...then add programs as you go along for a minimal, lean system. Also, check out ZenWalk...excellent distro, light on memory requirements...