out of loop for a while, need advice on upgrade

hey, it's been a while since i posted here, but i'm back. For the past 6 months or so my computer has been revolting against me and has made me run in circles trying to figure out what is wrong. What happens is that i get random memory read/write erros and if i right click on something the menu won't appear, or if i open something toolbars will be missing or filled in white, or programs won't open at all.

I'm not posting here for a solution to this problem, since i don't believe there is one. I've replaced the RAM tried a different video card and ruled out a hard drive or software problem. The only thing left in my mind is the motherboard.

Since Asus does not do cross shipping for their warantees and i simply cannot have no use of my computer for 6 weeks as i use it for work, it seems as though my only choice is an upgrade, unfortunately a lot has changed in a year and a half.

I currently have:
Asus A7m266
AMD athlon 1.4ghz
2x crucial 256 mb pc2100 ram
2x ibm 60 gb 60 gxp raid 0
1x wd 1200jb 120gb
leadtek gf3
intel 1000/mt
enermax 430 watt psu

question, should i upgrade my motherboard AND my cpu, or just my mobo. I don't really want to change the RAM unless it's cheap enough and beneficial, my main concern is getting rid of anything that could potentially be causing this problem.

As for what motherboard to get, this is where i need help, mainly in choosing the chipset. VIA, Nvidia, other? Not sure what's currently the best route to go. I have built systems recently with asus a7v8x with good results, but wanted to check to see if there's anything else that would be better suited.

Now as far as the cpu is concerned, if i am going to replace it, i don't want to spend more than $100. The 3000+ had me interested until i saw it's $560 price tag (since when did AMD prices look like Intel's? Should i be worried about the future release of clawhammer, or will it take some time for the 64-bit technology to be perfected?

I'm basically being being forced into this upgrade so i don't want to spend that much money, a crash course in what should be looked at and what is coming up would be great.

Thanks