UI-View is a Windows APRS program. This application differs from most APRS software in that it isn't designed just to be used with TNCs in terminal mode. UI-View also supports TNCs in KISS mode, AGWPE host mode and BPQ host mode. The 32 bit version of UI-View also supports WA8DED/TF host mode, and the variant of it used in the SCS PTC-II and PTC-IIe.
The host mode support means that UI-View can be used with an extremely wide range of packet hardware and allows up to 16 RF ports to be used.
UI-View32 is a 32 bit version and so needs a 32 bit version of Windows - Win95, Win98, WinME, Win2000, WinXP. It is for registered users only, and has many extra features compared to UI-View(16). If you are unfamiliar with UI-View32, you can try UI-View(16), but unless your hardware doesn't meet the minimum specs for UI-View32, the 32 bit version is recommended. The absolute minimum hardware spec to run UI-View32 is a P120 with Windows 95, 98, ME, 2000 or XP. If you run it on anything less than that, then it will be very slow.
Don't expect to be able to run PMapServer7 on a P120. Undertow's own "minimum spec" is for a 200 MHz Pentium, but you will get better performance by running it on a more capable machine. A 500 MHz machine will run PMapServer7 a lot more smoothly than one that only just meets the minimum requirements.