Pentax has made lenses in 2 different types of mounts: the "pentax screw mount" also known as the "M42", "Zeiss Screw mount" and "universal screw mount" and the "K" mount, which is a bayonet.
Anything that says K mount, including the original "K", the newer "Ka" and newer yet "Kaf" mounts will fit with your camera.
It is possible to use screwmount lenses on the camera with an adaptor. I'm thinking the SP-K is the adaptor and the K45 mount is the regular K mount, but I have never heard of either names.
Note that lenses that have an "A" on the aperature ring will work with virtually every function on the camera. If you are looking for a good deal on some really fine lenses, lenses without the "A" can be used only in manual mode which does stop-down metering; which is much more accurate than traditional metering. However, you lose functions such as multi-matrix metering and it will take a longer and more effort to take a picture. However, newer lenses will allow you to use all functions. A bonus over the canon is that pentax lenses usually go used for much less than Canon lenses, which seems to be the vogue these days.
Since the kit lens is so cheap (partially substidised by the camera body) it would be worthwhile to pick up the kit lens and invest in a few old primes. The kit lens will do fine for snapshots and the primes would come in when you are feeling creative. (I'm assuming the camera isn't only used for vacation snapshots etc) The primes will give you better corner to corner sharpness, will be faster for low light, and have much more pleasant bokeh.
My advice would be to try it first, and make sure that there is a refund policy. There is little possibility you can get comfortable with the camera in a couple of minutes in the store, so if you could, buy the combination, try it to make sure you get the hang of it and before long it should be second nature. There is no substitute for experience in this situation.