Assuming your IDE drive is connected (and if you aren't using a 64-bit capable filesystem, under 4G), your first port of call is HDToolbox.
On opening HD toolbox you should be presented with a list of the drive device interfaces (unless your HDtoolbox icon has a device = xxx.device tooltype set already.
The IDE drive should show up under scsi.device. If the drive is completely unformatted (as far as amigaos goes, I mean), it will probably tell you the drive needs installing, you should just click on proceed. It will read all the default information it needs from the drive (size, cylinders etc.) itself.
Once the drive is "installed", you can select the scsi.device in HDToolbox and your new IDE drive shows up. Select it and go to "partition drive" to partition it to your liking. It's a good idea to keep your OS partition below the 4G limit, even on 64-bit capable filesystems ;-) Besides, anything over 200Mb is total overkill for OS3.x + utilities :-)
Partitioning is relatively hassle free and you can just drag resize partitions you are making.
Once your drive is partitioned the way you want it, reboot and you can format the newly appeared drives as normal. Better to quick format them than normal format however. Also, if you are using the normal amiga file system (ie not SFS or other third party), definately give "directory cache" a miss for hard drives. It might speed up floppies but is counter productive on hard drives :-)
