This allows one to use the flash in combination with shutter speeds faster than the camera's sync speed, which in current Pentax models is 1/180th of a second. At shutter speeds exceeding that, there's never actually any time when the entire sensor is exposed at once: there's just a fast-travelling slit between the front and rear shutters. HSS works by creating many very fast pulses rather than one bright flash, so the tradeoff is reduced power. This isn't necessary (in fact, quite the contrary) for freezing motion — for that, you need to look at the actual flash duration (which is generally much, much shorter than the shutter speed).
The Pentax AF360FGZ and AF540FGZ can do this, as can the Metz 48 AF-1 and 58 AF-1 models and the Sigma Super variant. Sigma calls it FP flash (for focal plane) instead of HSS.
The Metz 54 MZ-4i has the ability to do HSS with some systems, but not currently with Pentax and the SCA-3702 module.
Note that HSS can be used in combination with wireless P-TTL, but not when using the camera's on-board flash as the controller1. This may simply be a software limitation due to user interface design — wireless flash mode and high-speed sync mode are separate choices one may select from the various flash modes, rather than being independent switches.
The Metz 58 AF-1 also has this limitation due to a bug in the current firmware. There are currently no known plans for an updated firmware to fix this issue. It works in HSS mode as a slave, however.
