|I will jump in here. First off the reason for the price of anything is the cost to manufacture. The way hard drives are getting more capacity is by increasing the arial density of the media itself. |
Once the manufacturer makes the change to higher arial density it stops manufacturing the lower density media. Just as older RAM types have gotten more expensive, so have smaller capacity drives.
No on to your real problem.
The change from 28 bit LBA compliance (127/137GB) to 48 bit LBA compliance (144 petabytes) meant that if you have a 48 bit LBA compliant BIOS and OS you could use most any hard drive available.
Unfortunately this isn't always the case. Desktops running later versions of Windows sometimes have problems configuring hard drives in the 1/2TB range. The reasons for this are elusive but the issue does exist.
Then there is the issue of SATA I vs. SATA II. In most cases SATA II hard drives will default to running at SATA I speeds when connected to a SATA I controller. However this isn't always the case. For that reason 3.5" SATA II drives MAY come with a jumper to throttle to SATA I speeds for compatibility.
In the case of Laptops the BIOS is usually much less flexible. As eluded to above the BIOS version may need to be upgraded. Or your laptop may have a SATA I controller and virtually all current SATA hard drives are SATA II.
If WinXP can see about 237GB but the BIOS only sees 150GB I would not recommend running the laptop that way because you may end up with data corruption or loss.
It sounds like you haven't yet purchased a replacement yet. I recommend you go ahead with the 250GB. When first booting watch the POST screens to see if the BIOS is recognizing the new drive by both model and FULL capacity. If that happens then you are good to go.
If your version of WinXP contains NO service packs then you will not see the full capacity because as DAN as stated original WinXP is not 48 bit LBA compliant.
You have two choices at that point. First is to partition the drive at WinXP installation time to something less than 127/37GB and then after installation and updating the service packs you can configure the remaining space through Disk Manager.
The second method is to slipstream the latest service pack into the files on your existing WinXP CD and then burn the resultant file to CDR. Then install using that CD. Additional files can also be slipstreamed at the same time if desired.