You have at least two options.
Option 1.
Please refer to MS KB article 307545 that explains: How to Recover from a Corrupted Registry That
Prevents Windows XP from Starting
http://tinyurl.com/o5u8
This is quite lengthy and you have to be very meticulous.
Option 2.
Purchase ERD Commander 2003 that does System Restore when the Windows is not bootable.
It may be a little pricey but well worth it.
Reinstalling Windows on top it may not work because installation process will not see any previous OS.
It is good idea to back up your data before you try the above. You can use NB HD adaptor (2.5" to 3.5") to access your NB HD from a Desktop if the NB HD can be taken out. Or use ERD Commander 2003 Remote Access.