Hello there. Here is a list I compiled. See what you think...

Video Cards
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121219 $90 This is good
or
http://www.newegg.com/Product/Product.aspx?Item=N82E16814145151R $90 This is good
or
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127365R $80 This is not as good but ok

With these gfx cards, the memory interface width is expressed as 128bit or 192 bit or 256 bit wide. The bigger the better, and this parameter has a significant effect on performance.

Im going to suggest that you get an Intel Core 2 CPU because they are the fastest CPUs at the moment and you also want a mobo that can do you for a couple years with expansion potential for newer cpus. So here is a suitable mobo and CPU:

Motherboards (P35)
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131278R $60
or
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128337R $60

CPUs:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116070 $90 (equivalent to Athlon 5000)

I know its a bit more expensive, but you need to pay a little bit extra to go Intel. Sorry ..., but worth it in the long run.

The RAM you specified is fine

Thing is, with Intel you can go later for E7200 or E8200 or even Quad cores Q6600 or Q9450, but that will be impossible if you buy an AM2 mobo, unless maybe you have hopes of running a Phenom.

Thanks for that enlightemnet Swehunt. Ok, he could have Core 2, but still, its a rubbish PSU if its only 300W.

Is this your PC? http://www.ciao.co.uk/Dell_Dimension_E520__Review_5615804

If so, than you've got a Pentium D Dual Core which is different from Core 2. Closer to Pentium 4 in performance. But still, from that article, it appears you have a PCI-E slot after all. In that case get an ATI 4850 card. Best all round mid range card. And from the previous post. Yes, there may be some concern over your PSU. Hopefully it is a standard shape one which you can replace by purchasing anywhere. With 300Watt its going to get pushed once you put your new graphics card in. Like the old saying goes though, "Try before you buy"......

First of all you need to keep in mind that updating the BIOS carries a certain element of risk with it. In the worst case scenario, you can end up with a broken motherboard. Don't update the BIOS if you don't need to.

A good way to flash BIOS is:

1) From Windows download correct BIOS file from manufacturers website. If the downloaded file is a .zip file than you need to unzip this.

2) Copy (unzipped) BIOS file to a USB stick. (Leave USB stick connected)

3) Reboot PC and go into BIOS

4) From BIOS run Flash utility

5) Select your USB stick as the source drive

6) Select the downloaded BIOS file as the file you want to use for the update

7) Select yes and after you confirm that you want to proceed and the program is satisfied that it is dealing with a valid BIOS file, you will see progress bars as the BIOS is updated

Once you select yes , DO NOT DISTURB this process in any way. Although , with Gigabyte boards, if things do get messed, they can usually be restored from a backup BIOS, on other boards, if there is a problem, the motherboard can be wasted. Once it has finished, you will need to reboot. If you reboot successfully, observe the BIOS messages as they flash by, and you will notice the new BIOS version number.

Job done....