There is no missing space since a WD 250gb ide hard drive normally sees 238.4gb approximately after the some space is used for master boot record if there's an OS installed and the means of partitioning. The lower total drive space is what is available for immediate use. Take an old dos boot floppy and change to the prompt for the drive if you can get sata drivers loaded and type the dir command to see the actual figure climbs over 250,000,000,000bytes
Drive totals in 120gb, 160gb, 200gb, 250gb, 320gb, and others is more or less a rounded figure not a conversion method used in math to calculate actual drive space. Everybody gets a bug in their craw when first seeing the apparent discrepancy and thinking something is wrong. It isn't! The rounded figures are more for marketing reasons and not computer science related totals.