2000 Pro is a very good OS, however, XP is more than just the new thing, I work in the IT department at a life insrurance company, and work on computers with every OS from windows 95, to XP Pro.
2000 will work well for everything you want pretty well, but,
XP Pro makes everything so much easier to use, setup, use with any periphial, work with networks, and keep up to date and running great than 2000. In your case, I believe this depends on what hardware you are planning on running with the OS.
Everything from the stats of your MOBO, to your memory, and the CPU you are planning to upgrade to, will depend on how your system will run.
XP does not run differently because of "fluff," as mousepad so called it, XP can be tweak to hell if it is not running like you want it, you can disable countless resource-using settings that will stop the un-needed usage of resources.
Are you planning on purchasing XP Pro if you decide on using it? Or do you already have it, or will be recieving it from a friend? It sounds like XP is for you, but post your stats on your motherboard, and the memory you are planning to upgrade to, and the CPU you want to use, post what you have now, and what you will have after the upgrade, that info may help with your decision, based on what people think on here.
Hope this helps,
Blake