No connectivity to the internet

Hi. I have recently reformatted my hard drive and installed Windows XP Professional x64 onto my PC (Windows Vista x32 was previously installed).

My PC (Dell) originally came with Vista but I had lost the installation CD (along with the drivers CD), so I used my old copy of XP Pro to reformat and reinstall. Everything was wiped when I had reformatted my hard drive, including my drivers. But now because of this I am no longer able to connect to the internet through my PC.

I think the main reason is because my "Ethernet Controller" needs an updated driver. But I have lost the drivers CD that originally came with the computer. When I try to download the needed drivers from www.dell.com and install I get a message saying the driver is not supported by my operating system, thought in the "Compatibility" tab it clearly states that the driver is compatible with Windows XP.

Does anyone know what teh problem is, and what I should do about it?

Thanks for any help.

Computer:

Dimension E521
AMD Athlon II x64 Duel Core
4GB DDR2 RAM
500GB Hard Drive
Windows XP Professional SP2 x64 Edition / Windows Vista Home Premium x32

The drivers are for XP 32 bit, not 64 bit. This was the problem with XP 64 bit. With the popularity of XP 32 bit and the impending release of Vista 64 bit, there wasn't much support put into XP 64 bit.