Need some help selecting Mobo, CPU

I have a Dell Dimension E520 that it appears the mother board has gone out on.
Currently it is set up as such:
Dell Dimension E520
1 Graphics Card, VGA EVGA 512-P3-N801-AR 8800GT 512M
2 Dual In-Line Memory Module, 512533M, 64X64, 8, 240, 1RX8
2 1GB (1X1GB) PC25300 NONECC UNBUFFERED 240 PIN DDR2 DIMM
1 Windows Xp
1 Serial Ata Optical, Matrix, smith, mini Tower
1 Processor, 805, 2.66, 2MB, PentiumD Smithfield For Desktops, B0
1 Modem, V.92, Data Fax, Internal SON2
1 DVD BURN SAMSUNG|SH-S203B
1 Digital Video Disk Drive, 16X, Serial Ata, Half Height, Philips
1 Hard Drive, 160GB, S2, 7.2K Samsung
1 Hard drive 160GB Western Digital
1 Power Supply PSU OCZ|OCZ700GXSSLI 700W RT

I would like to be able to use as much of the old PC as I can while replacing/upgrading the MoBo and the CPU. If I would be better server upgrading the memory I can do that, I just need some help figuring out what will go with what. Thanks.

I like Gigabyte search ebay or newegg.

Thanks but I went ahead and did a complete new build using a MSI 890FXA-GD70.