It will report 137GB. For operations within windows PM is fine, but as soon as it needs to reboot and use Dr DOS or Caldera DOS (can't remember which) it will only see 137GB and therefore if the partition in question strays across this...
XP does very basic operations: create, delete, etc... PM and others do more complex operations such as resize, move, merge, etc.
Be very careful though (as mentioned, a full backup is wise) and if you are using a 160GB or greater disk...
Don't really know much about this side of things but from straying from other areas I know you will probably want something more than a mic plugged straight into the laptop, best head over to more closely related forums for advice....
Oh right, well in that case you will have to look elsewhere, Dell don't make one for us.
Check out the huge thread about this, at least a couple of sellers there (well, there was last time I checked).