Intel 845D chipset supports registered SDRAM and DDR both.

The CMI 9738 supports 4 channel with additional Dolby Digital decoder, If you select 4-channel, Line In will be reconfigured as another Line Out to support second pair of speakers.

No, please don't mix  SDRAM and DDR memory modules at the same time. Otherwise, the motherboard may be damaged.

No, please don't mix the DDR and SDR memory at the same time, otherwise, the motherboard may be damaged.

Yes, the P4IBASD V3.0 comes with VIA VT6202 chip which supports USB 2.0.

No, the P4IBASD V3.0 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.

Yes, P4IBASD V3.0 supports Intel Pentium4 CPUs with front-side bus (FSB) speed up to 400/533MHz.

P4IBASD 3.0,maximum CPU and HDD supported information as below, HDD:250G Pentium 4 400Mhz FSB (256K/512K L2 cache) CPU – 2.6G. Pentium 4 533Mhz FSB (512K L2 cache) NW CPU –2.66G Mhz Pentium 4 800Mhz FSB (512K L2 cache) CPU –No support Celeron 400Mhz FSB (128K L2 cache) CPU – 2.8G Mhz Pentium 4 533FSB (512MB/1M L2 cache)HT CPU – 3.06G Mhz Celeron D 400Mhz FSB (256K L2 cache) CPU – No support