Deciding from the following chipsets

I'm trying to figure out the best upgrade path within my budget.

I'm going to be getting a 9800GT/4350 or 9800GTX/4850 card. I'll leaning towards the 4850 right now.

Processor and board? I can't do Core Duo for Intel so I'm guessing a P45or P43 (I don't know if the Q series (45) is better or not). On the AMD side I can do the 64 X2 whereas it seems like the Core Duo is the equivalent match on the Intel side but alas they are a lot more expensive, at least for my budget anyway.

So to that end, there are a few AM2+ boards under $100 (or close to it) like the ASRock AOG790GX, Foxconn A7DA-S or Biostar TFORCE TA790GX3.

Once I pair this with 4 Gigs of memory on my current XP machine I'll have a much faster system than I currently. Even though I can play most of the newer games on my older system, just not with all the eye candy turned on (Call of Duty: World at War, Crysis, Fallout 3). My old system runs on a Biostar M7NCD Pro board with a Socket A 3000 processor, a X1950 Pro AGP card and I was running 1.5 GB of DDR ram. As I only have a 19" CRT moniter I don't need to worry about the super high resolutions of my games.

As I'm happy now I can't imagine why I wouldn't be happy with my above wishlist. But, having been out of the upgrade game for awhile now I don't know if there are any caveats I need to look out for with my choices. I'm only upgrading as it is because I'm on the brink of not being able to play the games just about to be released and because I'm having problems with my memory slots and getting memory sticks to work right.

So, pros/cons of my choices?

+1 - I would go P45 and E7200, E8400, or E5200 (budget) and get a 4850.

^ Correct. I think OP was comparing 4830 and 9800GT.

+1 for P45 + E7200/E8400/Q6600 + 4850 + a good PSU (ie PC Power & Cooling, Corsair, OCZ)

either take the biostar or asus, asrock is more budget oriented and often fail at oc'ing. most ppl would recommend the p5q, its very popular