Okay, well can we get a little more information about the power supply. It may not be in for a 8800GTS. Can you let me know the rails on the 3.3V, 5V, and +12V lines? (They will be on the side of the PSU)
The DDR2-533 memory will severely limit your overclock. In order to get 3.0Ghz for your E6300, you will need a FSB around 428Mhz. That means your memory will need to be running at DDR2-856! You can always upgrade the memory though.
Edit: Do you have any more info on that 250GB SATA drive? Who makes it? What model? How fast? How much cache? SATA 1.5 or 3.0? That can help a lot!
With your current components that you already have, here is what I suggest.
This will provide you with a higher multiplier so that you can get a higher overclock with your memory. Now you only need a FSB of 375 (DDR2-750) to obtain 3.0Ghz.
ASUS P5B Deluxe $179.99
Simply the best overclocking Core 2 Duo board on the market.
Your Memory For Now
I suggest Crucial DDR2-1000
when you can upgrade. Best memory for the price.
EVGA 8800GTS $399.99
EVGA has the best warranty, RMA, and upgrade options of them all.
2 x WD 160GB 7200RPM 16MB Cache SATA3.0 $62.99 each
You will be amazing how fast games loads and Windows start up with these in RAID0. Remember, you will need a floppy drive to install RAID drivers.
Your PSU for now
I suggest an SilverStone ST75F
750 Watt PSU when the time comes.
Sceptre 20.1" LCD $199.99
The best monitor for the money. I also have this and it is beautiful. If you want to see what I had to say about it, go here
A Turniq Tower for $52.99 or a Scythe SCINF-1000 for $47.99
Turniq Tower is regarded as the best air cooler on the market. They are hard to find and sell fast!
Save money by dropping the 2nd harddrive or by going with the E6300.