Can I put an HP hard drive into a Lenovo?

First, I doubt the drive was made by HP, as most buy them. Second, the specs on a 'drive bay' are pretty generic, and most will interchange. So, if they are similar sized computers, odds are good.

If it fits and the interface is the same (SATA or IDE), then you can use it. However, you will have to erase it and re-install Windows if you want it to boot Windows.
You can just use it as a secondary disk regardless (and read your old files).

Yes, it can be done.No, it isn't as simple as you'd like… The old drive is bootable and Windows won't allow two bootable drives in same system, so you have to disable the boot from the old one.

this needs an idiot utility that runs from DVD or USB and to which you boot in order to turn off the bootable nature of the old drive. Try hard disk utilities at downloads\cnet.net… Might be a free one can do that -- it's a pretty simple task

Well, it will work with the lenovo, but you won't be able to boot into the windows that was installed on the HP laptop because of the special drivers, as in not only are the drivers for a different name brand meant to work on a computer with a specific BIOS I.E. Make and model, but the Lenovo has its own windows drivers made specific for the BIOS in the Lenovo laptop.

So in short, you can actually use the hard drive like a backup to recover data and store new days of some sort, you just can't boot into windows installed on the HP hard drive.

Its probobly best to find out what kind of hard drive it is and what kind of connection it needs, then simply find an external Hard drive enclosure, like a rocketfish for like 10 bucks from amazon or something and then do that.