Hard drive swap

[EOD]

Hello, I would like to take a hard drive out of a trashed laptop, and install it on either another laptop or on this tower computer, and be able to use the operating system on it. All the equip is Dell and all the OS's are XP When I plug the hard drive into this tower (desktop), I can only access it thru windows explorer, and then its only files like "User 1" " All users" "Program files" Etc...- a lot of stuff seems to be inaccessible. Id like to just basically connect the old drive with a USB  and have the thing work normally, or install it in the laptop, and have it work... When I swap hard drives in the laptop, it wont boot up. Sorry if this question is poorly worded, but its the best way I can figure to describe what Im after. PS The hard drive Im looking to use is in good shape, and was working when I pulled it out of a laptop that got its screen trashed.
Thanx L 
 

[Allan]

Not quite sure what you want to do. You cannot use the old hd in a different system and boot to it without reinstalling the os. But if you want to use it as a second hd that's fine.

[EOD]

So theres no way to make it boot up without re installing the OS? Rats....

[EOD]

That was sort of the whole point of the swap....

[Allan]

No. You cannot take an HD with an OS from one system and expect a second system to boot to it unless the two systems are identical (hw).

[Salmon Trout]

No. You cannot take an HD with an OS from one system and expect a second system to boot to it unless the two systems are identical (hw).

Even then with a Microsoft OS you would most likely run into activation issues since the unique hardware ID would have changed. Linux would probably not care.