Does it fail with a specific error or just get hung up in the boot process...is the same true for booting into safe mode ?
If you feel like repairing rather than re-installation then generally XP will hang on some issues with the registry..corrupt disk..faulty hardware and report a specific error for missing files.
Depending on the reason for it not booting...i.e if the registry is corrupt or miss configured, there is an offline method to recover the registry from a system restore registry snapshot (assuming system restore was running..it should be).
All you have to do is access the disk from either another machine or a live boot disk...gain access to the System Volume Information folder and copy the registry hives from the last known good snapshot..ie one with a file creation date from when the machine was known to be working (REGISTRY_USER_SYSTEM, SOFTWARE, SAM, SECURITY, DEFAULT etc) into the location of the current registry (c:/windows/system32/config) and then rename them to the same as the current files (from REGISTRY_USER_.DEFAULT to DEFAULT etc)...take backups of the "broken" registry hives before renaming the snapshot ones if you are feeling unsure about this.
There is a microsoft KB article on how to do this here http://support.microsoft.com/kb/307545 however that assumes that the only way you have to access the volume is via the recovery console on your installation media...if you have a live CD booting OS that can see NTFS you can ignore the steps regarding putting the repair registry in place first because you should be able to get to the system volume information folder from a live CD (you can't from the MS recovery console)
If you are trying to do this from another windows machine then you probably also need to look at KB article 309531 but this isn't relevant if accessing the volume from say a linux live boot.
Otherwise if you just want to copy the data off...
Modern laptops tend to be SATA now and the drives use the same connectors as Desktop SATA drives....otherwise you can buy very cheaply either converters that convert 2.5" IDE harddrives to the standard 3.5" connector or usb converters that accept 2.5" drives.
Another thing worth mentioning is that sometimes (particularly when disk failure is imminent) windows can corrupt it's own filesystem to the point it can't even load chkdsk..so sometimes if you have a strange boot error it can be worth booting the recovery console from some installation media and running a chkdsk /P c: before trying anything else.
In either case if you get a working machine after following either of these steps I would strongly advise running smartmontools against the disk to see if there is a hardware failure causing the data loss.