It seems that your PC will be used for the more or less regular desktop applications. For those systems an Athlon XP or slower (standard) P4 would suffice. If you want to go the future proof way, I’d avice a Athlon 64 running at either 3000+ or 3200+. Most likely, the Athlon 64 mainboards will stick around for some time and CPU upgrades will be possible.
A videocard? Well if you are not a gamer, the cheapest videocard (maybe onboard) is sufficient. If you want to do some gaming, get a card like the Ati Radeon 9600 or so. Those cards perform reasonable right now and will be enough to game for some time. No top speeds, but still good performance for the money!