The 955BE quad core is less expensive than the 1100T 6 core. Tom's Hardware ranks it about the same in their hierarchy charts, although it is a little behind in actual benchmarks. The 955BE also lacks the turbo mode included in the 1100T, but is still overclockable. Given your older motherboard, you may wish to weigh the pros and cons of overclocking. As board components age, their ability to handle overclock diminishes.
Visit the ASUS web site and locate your motherboard. There will be a download tab. Download the most current BIOS for your MB, along with BIOS utilities. They will have readme files as to their operation.
If you have a CD that came with your motherboard, it may have the BIOS utility already on it. Many of these disks are also bootable so you can try that and see what comes up. I cannot recall if ASUS has a Windows utility program for this.