L4IBAE v1.x, maximum CPU and HDD supported information as below,
HDD: 250G
CPU: Pentium 4 400Mhz FSB (256K/512K L2 cache) CPU – 2.4G
           Pentium 4 533Mhz FSB (512K L2 cache) CPU – 2.8G
           Pentium 4 533Mhz FSB (512MB/1M L2 cache) HT CPU – 3.06G
           Celeron 400Mhz FSB (128K L2 cache) CPU – 1.8G 

Intel 845 series chipset does not support Registered ECC memory. However, it supports both ECC and non-ECC memory.

Yes, the L4IBAE V1.0A supports Intel's Hyper-Threading technology. If you install a CPU with Hyper-Threading such as P4 3.06G on this MB, there is "Hyper-Threading technology" item in BIOS to let you enable or disable this new feature.

Yes, the L4IBAE V1.0A comes with Intel ICH4 chip which supports USB 2.0.

No, the L4IBAE V1.0A supports AGP mode up to 4X (1.5V only). You can install an AGP 8X card on this MB but the card will run with AGP 4X mode.

No, the L4IBAE V1.0A supports DDR RAM up to 266MHz.