Outdated? Everything you can buy will be outdated in 6 months. But that's the way these things go, so a better question is will it still be able to perform the tasks you need in a few years?
I would be half-tempted to say wait a few months for both AMD & Intel's sockets changes, PCI-Excpress, (and the accordingly new graphics cards), let serial-ATA get even more established, DDR2 memory, blah blah blah.
Forget that.
First, you don't want to be the guinea pig for all this new technology. Second, it will more than likely cost an assload of cash.
I would say go for a A64 3000, running just over $200 at newegg right now. Fast, cheap (relatively), and if (when) 64-bit software becomes prevalent, you'll be set. Should be better for hanging in with software longer than the Athlon XP's.
Memory wise, follow the above posters ideas, I personally like Crucial, I haven't had any problems with them (yet--knock on wood).
As far as a motherboard, you may as well poke around Anandtech and Tom's Hardware for reviews on A64 mobo's. Head over to newegg, they usually have links to reviews on the products they carry, for a wider range of reviews. You might want to get a fairly loaded one, to keep from limiting you later (i.e. Firewire, SATA, upgraded onboard sound).
I like Albatron, haven't had any problems with their products yet, and good performance.
Might want to head straight to a SATA drive, has the benefit of wee little cables
What video card you get is a whole new topic (for the video forum), and don't forget to get a good case and power supply, everything you put in your brand new pile of expensive electronics will be running off your psu. Don't skimp (and you probably have picked this up already, the wattage number isn't the end-all for psu's, get a good brand).
Good luck, and you'll be happy when it's all over with. Of course when you realize you built a computer yourself and it works, you will be upgrading as often as you can *insert force suggestion here*.