Really? That's great. It's true what I ran XP on was an older box. PCI cards. Older model. Didn't see portrait mode offered.
I recall a few monitors stating "portrait" mode. If the monitor has a stand which rotates to portrait position, then the monitor supports it. All you need then is a video card which does.... even if the monitor stand does not rotate, still might support portrait position in a VESA mount. Nvidia's NVS does, of course. (Landscape position is the default and portrait rotations are selected through the NVS driver.)
spam for micro center, lol, took them about 10y to add me to their mailing list, I think their mailing list run on Commodore 64.