You should be able to just plug the drive into a spare SATA port in the Mac Pro. Newer versions of OS X can read NTFS, they just can't write to it. So data retrieval shouldn't be a problem. 2.5" and 3.5" drives use the same SATA connector.
Afterwards, you can just leave the drive in the Mac Pro. Format it using the Mac disk utility. That'll convert it to Mac format (HFS+) and you can treat it like any other Mac disk. Buy a 3.5" to 2.5" mounting bracket for $5-$10 if you're not comfortable with the drive flopping around inside.
If you really want to make it an external drive, you need to get an enclosure. I'd recommend USB 3.0 for both price and compatibility. Those will cost you about $20-$30. If you format the drive as exFAT, both OS X and Windows can read/write to it. I hear it's better to do the initial exFAT format under Windows. If you format it as NTFS, Windows can read/write to it, but the Mac will only be able to read it. It won't be able to write to it unless you buy special software. If you format it as HFS+, the Mac will be able to read/write it, but Windows will not be read/write to it unless you buy special software. Save your money, format it as exFAT.
If you're made of money, you could get a $150 thunderbolt enclosure. But since this is a HDD which won't come near the ~300 MB/s transfer limit of USB 3.0, there's really no point.
Edit: If you're feeling particularly adventurous, you could convert the HDD to a vritual machine before reformatting it. Parallels can convert VMWare virtual machine files (.vmx). You'll need to find another PC for the transfer. Install VMWare Converter on the PC. Plug the laptop HDD into it, Run Converter to create a virtual machine image of the HDD.
Transfer that file to the Mac, have Parallels convert it. Then you can "boot" your old laptop inside a window on your Mac if there are any programs or files you needed to access. I actually do this on all the computers I help people upgrade now. Saves me from a frantic call 2 weeks later where they tell me they absolutely need a program that used to be on the old computer's drive which we formatted. (Bookmarks are the most common thing I find people forget to copy.)