Do not overclock you computer until you find the results of what you said you were going to test
One of them:
Using onboard audio
I think the problem with your setup is that you start tweaking before you get things stable. THAT IS THE ISSUE! Leave everything at stock Go into the bios and select optimal defaults. Test from that. If it's not smooth and it still stutters, don't overclock as your problem is related to something else. Example, "I overclocked and it was better but much worse" or something to that affect. Either you expect to much and/or you machine is not configured properly.
Also do not use 3rd party drivers until you have things stable.
The biggest problem I see is not the hardware it's the person using it. I get the vibe that you want the "console experience" as in plug it in and it works. If you wanted that you may have been better off going with a Dell or a console as many people recommended already. Honestly everyone needs to start somewhere but you need to stick with stock until you know what your doing.
In my opinon I think you are expecting a little to much in combo with your machine not configured properly. Your video card is on the high side but the rest of your machine is on the mid end (1GB memory and a 3200 is not what I consider high end). Example, some games you say are running ok (still not acceptable) with no AA but other games you are running it with 6AA and have the same opinion. How is the game at 2*AA? Which leaves me under the impression if the game ran good at 1280-1024 with 4aa you would still have a problem that it doesn't run at 1600-1200. So in summary even though you have a high end card don't expect it to run with everything at 6X aa. Example I have a X1800XT 512MB card and I run company of heroes with 1280*1024 with the game AA on. That is the breaking point for me, as in any higher it runs like crap. It performed:
"Good"
AVG 36
MAX 137
Min 12.6
This is with a single core Opteron 2.7GHZ (vs your 1.8GHZ) and with 2GB (vs your 1GB).
To start out most of the games you listed have in game performance test like the one above. Example Company of Heroes, Fear, and HL2. Let us know the resolution you test it at (start with 1280-1024 no aa and progress upwards), make sure you sound options are set to low, test, and display the results. The reason of this is also due to opinion. Runs like "crap" is very subjective. So run COH and let us know the results.
Also after running each game run task manager, press ctrl+alt+del, and select performance. Note under Physical Memory (k) /Total. This your amount of memory installed. Under Commit Charge (k) look under peak, this is the amount of memory that was used at the peak. If Peak>Total then you are loosing performance due to paging and will either need to upgrade memory or reduce settings.
Good luck and people are here to help but you need to keep up your end and make sure you take the suggestions seriously. If you don't have time to test, then why should it be at the top of the forum?