I see your main goals are compatibility with your older hardware, and office software availability. Which means you'll need something that's rock-solid, with apps that "just work". So it sounds like you're about to learn some Slackware!
This is an optional step, but... download one of the available "live" Slackware-based CDs, like SLAX or others. It'll allow you to test-drive Linux without actually installing it on your hard drive or erasing any data. This way, you'll get a feel for how your hardware might interact with full-blown Slackware. (It'll also decrease the Slack learning curve, which is always a good thing.)
For a central spot to download any Linux CD you want (for free), try Distrowatch.com, if you have cable/DSL.
Now, be advised that Slackware Linux is no punk. Configuration will be tough your first time around but, like the previous responder said, that's part of the fun of learning "real" Linux. Use the online documentation and forums, and you'll be up & running in no time. And once you've got Slack set up the way you want it, your old hardware will love you for it.
You'll be able to run your Firefox, email clients & other office programs (OpenOffice, KOffice, etc.) with little to no trouble.
MS Office & many other Windows programs will run on Linux with the help of programs like CrossOver Office. CrossOver's not free, though.
And don't worry about your system requirements, you've got enough listed to run a basic Linux setup w/ browsers & office programs.
Hope this helps.
http://www.slackware.com
http://www.slackbook.org