A recent post on the Apple Discussion boards indicated one user's issues getting Mac OS X to properly recognize all 75 GB (actual capacity) of her newly purchased 80 GB hard drive.
As pointed out by subsequent posters, some drives require that you re-configure jumper settings in order to address the full capacity of your drive.
For instance, Western Digital maintains a page at http://support.wdc.com/techinfo/general/jumpers.asp with jumper setting information for its SCSI and EIDE drives. Other manufacturers generally offer a similar page, or documentation included with the drive providing the jumper configuration information.
Other World Computing provides an excellent compendium of PDF documents for:
- IBM/Hitachi Hard Drive Jumpers
- Maxtor Hard Drive Jumpers
- Seagate Hard Drive Jumpers
- Western Digital Hard Drive Jumpers