Need more info:
1. What are the model numbers for the Western Digital 160 GByte and 300 GByte hard drives?
2. What CD are you attempting to boot from (and why)? Western Digital CD? Microsoft Windows Installation CD? OEM Recovery CD?
3. PC Manufacturer/Model Number (if "Brand Name" computer), otherwise Manufacturer/Model Number of the motherboard.
4. Approximate manufacture date (month/year) of the computer?
5. Which operating system is the computer using (or will be using)? Windows ME or Windows XP?
6. Are you planning to reinstall the operating system onto the new hard drive in a single drive configuration?
7. Opinion. An older BIOS (date) and operating system may limit the size (capacity) of hard drive that you may access. Without loading special sector addressing software, you may be up against the 137 GByte limit. For example, I'm running Windows ME on an HP Pavilion 6736 computer manufactured July 2000. Because I decided not to use the special addressing software, I'm only able to access 137 GBytes of my 160 GByte Seagate hard drive. I did this to avoid corrupting my data should some well intentioned person slave the drive to another system to recover data without the necessary addressing software. I seem to recall both Western Digital and Seagate have information regarding the addressing limitation, but I can't seem to wrap my mind around the problem without getting a headache.
using a drive larger than 137GBMy unsolicited advice is to work with the Western Digital 160 GByte drive and if it gives you 137 GBytes without doing anything special, then take it and move on.