Solution :

That's the Promise onboard ATA100 driver which is searching for devices even more incompetently than the ATA100 BIOS. Get the latest Diver release (Version 1.60 Build 25 or later).

You can get the drivers at ASUS Taiwan Driver Page

Solution :

Disable the BIOS as described above, don't install drivers and disable the controller in the device manager.

Solution :

Directly after POST (Power On Self Test - the screen with the energy star logo) the screen blanks, then displays a message like "Searching devices" with a rotating slash and does so for up to 30 seconds.

This is the ATA100 onboard controller BIOS which searches for devices.
If you don't want to boot from a device attached to the ATA100 controller, disable the BIOS. This will still let you use all devices which are attached, but booting will be faster.

When using 1004a or later Bios : In Setup go to "Boot Menu" and set the option "Load onboard ATA Bios" (or something similar, anyway) to disabled.

1003 and older doesn't have this Option. But you can use a modified 1003 with the ATA100 BIOS removed. Look here for details.

Solution :

If you have TCP/IP installed for a network card, assign a fixed IP Adress (such as 192.163.0.xxx - with "xxx" being any number from 0 to 255) instead of having it automatically assigned.

In the latter case windows searches for a DHCP server while booting (and won't find one if you're not connected to a net which features one). This takes a few seconds, I guess about 15 to 30.

Use 255.255.255.0 as subnet mask.

Solution :

Defragmenting the harddisk is always a good idea :-) helps speeding up the boot process, too.

If you have WindowsNT 4, you can get a freeware defragmenter at www.oosoftware.de