how to power aopen mobo?

i noticed on the aopen website for the mobo im getting (ax45-v), there is a 4-pin power connector thats in a square. the psu i currently have is an atx, but it doesnt have the plug that the mobo has. is that necessary?

The extra 4 pins is part of the ATX 12V form factor for power supplies.

To state it simply, the Pentium 4 Processor requires extra current, and ATX 12V PSUs provide that.

Without connecting the 4 pin connector on the mobo, the display might not come, or your system might get unstable.

Better to change your PSU and give your system proper juice.

ok... so if something says "atx 12v", then it would be sufficient?

also, would it be possible to have too many watts in a psu? would a 400 w psu be good for a p4 mobo, hsf, 2 or 3 case fans, a floppy drive, and at least 2 cd drives?