I'm putting in a new HDD in a friends computer, I looked at it and the HDD was in its little metal box vertically. It was toward the front of the PC with the IDE (eww) ports facing straight up in the air.
Should I just get a regular HDD for this or do I need a perpendicular recording one?
A regular HD is fine, although most new ones will have perpendicular recording. "Perpendicular recording" refers to how data is electrically recorded on the disk and has nothing to do with the orientation of the case. I don't know if they have "retro-fitted" the technology to IDE drives.
It doesnt matter. The position of the HDD has no bearing on the recording technology. The only position that HDD are not recommended is upside down(This is in the old days and I'm not even sure if this is True on today's drives). Other than that HDD can run. I run my portable drives on different position (upside down, rest on it side, rest on short-side(side w/o the cable).
Majority if not all of the HDD today use perpendicular recording. Again it doesn't matter to your application or need. It will work regardless if you use perpendicular or old recording method.