External HD case for Compaq Presario 2100 HD

[Phaen]

I'm going to buy an external USB HD case for the hard drive that was in my old Compaq Presario 2100 laptop, and my question was how do I find an external case that will fit the HD?

I don't want to go ahead and buy one not knowing whether or not it is going to fit/work properly. Any input?

Thanks

[Adragontattoo]

PATA or SATA interface on the HDD?

[Phaen]

PATA.