Need suggestions to upgrade my gaming PC

So, I've been doing pretty good with my current setup for the last year or so:

2.14Ghz C2D on an Intel Reference Board (no OCing)
4GB of DDR2 RAM
BFG 7950GT Video Card

well, I bought CoD4... and um... yeah...
800x600 and it's dropping below 60fps whenever it gets nutty. Also, I seem to be getting a lot of flicker in the textures too.

So, I'm thinking of upgrading the video card and the motherboard to one that's more overclocking oriented. I've heard the E6400 can overclock... a lot.

I'm thinking of getting the 8800GT card and I just need to figure out which motherboard to get. I have a feeling the videocard will make the most improvement. Sucks when the BEST of the last gen can get destroyed by a game like this.

Ok, so here are the cards I'm considering

BFG Tech BFGE88512GTSE GeForce 8800GTS (G92) 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail

GIGABYTE GV-NX88T512HP8 GeForce 8800GT 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail

EVGA 512-P3-N801-AR GeForce 8800GT 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail

If you have the money, get the 8800GTS.

Is the E6400 your current processor now?

yes.
I'm thinking of getting the Gigabyte P35-DS3L motherboard and clocking it to 3ghz

Can't go wrong with that board.

How is your PSU? Will it be able to support an overclocked CPU and overclocked GPU?

Does your motherboard support 333FSB CPU's? If it didn't out of the box, check for BIOS updates that added support. If the chipset is 945, don't bother researching, but 965 or 975 chipsets most likely have native support with a BIOS update. You can do the BSEL trick with a rear window defogger repair kit & bump your CPU speed from 2.1 to 2.6GHz without getting a new board. Of course a new board & a better cooler can probably get you 3.2GHz or more.

you know. I need to check my PSU. I think it's a 600W

You should be able to push that chip to 2.8 - 3Ghz no prob. Just get a decent cooler.
The 8800GT will be a huge step up. You'll notice the most performance gain from this alone.