As the others have said, Partition Magic is by far your best bet to reallocate disk space from "D" to "C". $49.95 at CompUSA.
http://www.compusa.com/products/product_info.asp?product_code=313125&pfp=SEARCH
For the record, you might want to review this link:
http://www.microsoft.com/windowsxp/pro/howtobuy/choosing2.mspx
It sure looks like it was Sony's decision to not include Backup on the laptop, not Microsoft's. Also, the disk partitioning scheme was clearly a Sony decision. As a matter of fact, MS will use the entire disk in a standard defaut install.