First, yes your lenses will work on any Pentax DSLR.
second, any of the DSLR bodies are great value for landscape/ nature. The first generation all used the same sensor: a Sony 6mp CCD. The jpeg processing was updated over time. This is the Ist*D, ist*DS, ist*DL ist*DS2, DL2, K110D, K100D, K100D super.
The D,DS,DS2 have a larger viewfinder (pentaprism v.s. pentamirror). The D,DS,DS2 also support TTL flash v.s. P-TTL only.
The K100D (and super) have in body shake reduction. The K110 does not. all later models have shake reduction built in to the body, which works on ALL lenses such at the old lenses that you already have.
All these are great values. check the marketplace there are several kits for under $400.
The K10 added a Sony 10mp CCD sensor, the better viewfinder, and weather seals, but lost the AA battery support of all previous models.
the K20 updated the K10 with a Pentax/Samsung CMOS 14.6 mp sensor
The K200 put the K10 sensor etc.. into the smaller K100 chassis with AA batts and the pentamirror viewfinder.
Welcome to pentaxforums! check out the pentax knowlede base forum for resources (
Pentax Photography Knowledge Base - PentaxForums.com)
and you MUST check out the "boz" pentax database.
tell google you want "pentax boz"
you will find the most comprehensive compilation of pentax gear info imaginable. You can find all teh details about the gear you have at home, to compare with the stuff thats for sale... like the size/weight and close focus distance of those lenses etc..