Ok, that's an old KT133 mobo. The 1700 you have in it today is about the fastest it'll take. With a new mobo you'll definitely have to get new ram, the stuff you have is SDR, and today's mobos use DDR or DDR2.
I can see getting a new mobo/ram to use your existing CPU with the intention of upgrading to a faster CPU. But you're limited to the Athlon XP/low-end Sempron CPUs. They're still pretty quick (fast enough for doom3 - I played it on my XP2600+), but not current technology. That would run you maybe $150 (mobo and 1gig PC3200 RAM). You'ld use your existing video card and could upgrade to something better in the near future. Same with the CPU - can go up to an XP3200+ as long as their available (AMD has said they're not producing any more socket A CPUs after the end of this year). The downside to that is that that's it - you'll have to upgrade everything in a year or so when this system becomes not enough. (that may not be a bad way to go, so it's not a bad option)
A better option, IMO, would be to invest a little more now - you may end up getting most everything new - but you'll restart your 'piecemeal upgrade ability' with a socket 939 board, a lower end (but still acceptable) PCI-E video card, and a CPU that will outrun anything you could get for socket A. That would be an nForce 4 mobo (about 100), Atlon64 3000+ (150), 1gig RAM (80), GF6600 or X700 video (100). Probably will need a new Power supply (depending on your existing one), so allow an extra 75 for that. Comes to about 500. This will get you the best of the possible upgrade paths because 939 is the current high-end socket, so you can upgrade the CPU to a 4000+ or even faster in the future, as well as an X2 dual core. It also has PCI-Express so you can upgrade your video cards to the most current one when needed and not have to worry you have the old technology. Can even trim some off this option by going even lower-end on the video - but that's getting pretty close to the bottom of the barrel, and I doubt gaming will be very pleasant.
We could trim the cost of the 2nd choice a little more by dropping to a socket 754 system, but that puts you in the same upgrade problem - the 3700+ is the fastest 754 CPU AMD will make, and its AGP for the video card, so you'll be stuck there too.
Those are the 2 (3? - I don't see socket 754 as an option - might as well stick with the XP system in that case) options I see. Maybe someone else will have better/different choices.
Mike.
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