Linux is the kernel of the system.
The basic distributions are:
DEbian. This includes ubuntu and knoppix.
Redhat- included are SuSE and Fedora
Slackware
Gentoo
Yellowdog- this isn't really a separate branch but was the most compatible with the PPC architecture.
If you want support and are willing to pay for it the choose one of these and remember good support will cost a good amount of money. Choices: Mepis, Xandros, Redhat, SuSE.
If you want an easy installation then choose one of these: Ubuntu, fedora, SuSE.
SuSE, by the way, comes in both professionally supported and free versions.
If you want and are willing to compile your system then choose: slackware- moderate complexity some experience with UNIX is necessary, gentoo- it's all from source and could take days, debian- you can download and compile according to your preferences.
Windows 9x can easily be installed on a virtual layer if you want to still use the applications. You can also use win4lin, crossover office, and wine to implement many but not all w32 applications.
OpenOffice, StarOffice, and some Sun software are compatible office suites for you.