If you go AMD, keep in mind that your upgrade path is non-existant. With the 3.06 P4, you can upgrade later to a 3.2 or higher if that’s your fancy, but the Athlon in its current form is being EOLed by AMD with the introduction of the Hammer relatively soon. AMD does not expect the K7 core to scale beyond its current clock speeds.
If you go Intel, your upgrade path is to 4 GHz and higher with 1 Mb cache parts on the 90 nanometer process. In addition, they support larger and faster DRAM arrays than the Athlon and other features which make them highly desireable. Oh, and since you’re looking to the future, HT is a supported feature in most new games, including I believe Star Wars Galaxies. When an application supports HT, it utterly trounces the AMD processors.
Onto mobo selection, as the 130 nanometer process reaches the end of its useful life at Intel (just as AMD is starting to crank out chips using it, to give you an idea of how far behind AMD currently is behind the curve due to spending so much on the Hammer) at 3.33 or 3.4ish GHz, you can expect not to get much OCing out of these processors. To that end, I would suggest a board that is less about OCing and more about performance elsewhere. The Tyan Trinity i7205 sports AGP Pro, Gigabit Ethernet over its own seperate PCI bus to the northbridge, 5 PCI slots and ATA/100. In addition, there is also the Asus P4G8X Deluxe with IEEE1394 optional, Gigabit Ethernet optional and Serial ATA optional, and their only disadvantage is that all three of those options go over the same PCI bus as everything else. Those are probably your two best options right there. Both support 4 Gb of RAM and ATA/100 with 48 bit LBA (ATA/133 at ATA/100 data rates), 533 MHz FSB and the RAM is dual channel PC2100 DDR SDRAM, giving the effective bandwith of PC4200 DDR SDRAM, or a whopping 4.2 Gb/s. The addition of onboard GoC on the Tyan board on its own bus is especially attractive for LANs where you wouldn’t need to worry about PCI bus contention between that, hard drives, your sound card, etc sharing a bus. USB 2.0 is, of course, standard on both boards.
Onto the old ATi versus nVidia dilema, the ATi is a quieter card by a long shot and will not hog the next PCI slot to cool itself. In addition, the Radeon 9700 Pro has higher minimum framerates than the GF FX 5800 Ultra. Performance is a wash. The FX if faster with features disabled (such as AA and AF), but the 9700 Pro seems to beat it out in terms of “eye candy on” mode. Since I like eye candy, I’d lean towards the Radeon 9700 Pro, but that’s just me. Another thing to think about in conjunction with the Tyan board above is the AGP Pro 50. AGP Pro 50 allows 50 Watts of power to be deliverd to a card supporting that standard, eliminating the need for the external power plug-ins found on the GF FX and Radeon 9700. If price really is no object, then waiting a few weeks for the ATi FireGL X1 gives you a Radeon 9700 Pro core, no external power connectors and 256 Mb of RAM (compared to the 9700 Pro’s 128 Mb) to play with, in addition to more stable drivers and better OpenGL performance (albiet at a few percent reduction of DX performance, but the extra RAM should take care of that). Just something to think about, although at likely $1000 at launch it’s quite pricey.