I visited these parks in January 2003. I went first to the little town of Pagancillo. I could find neither package trips nor any form of public transport to the site but a local resident, Aldo, was happy to taxi me around in his pick-up truck, and at a very reasonable price too.
We visited Ischigualasto first, Aldo advised that the light was better earlier in the day. Here visitors' vehicles are organised into a convoy and then led around the site by a Park Guide. Frequent stops are made and things of interest pointed out and explained. Although this was said to be the rainy season there was very little substantial vegetation, it's a semi-desert, in parts rather like the Badlands of Dakota but perhaps not as colourful.
There are some remarkable and highly dangerous looking columns where a hard rock capstone protects and is supported by a tapering towards the bottom pillar of softer rock.
There is a feature known as The Ball Court where large, almost perfectly spherical stones have been formed by windblown sand sticking to an inner core.
While Ischigualasto is perhaps of most interest to those with a serious interest in geology, Talampaya is more picturesque. Here the park rangers provide the transport and in about 3 hours will show the visitor petroglyphs cut to exploit a remarkable blue deposit on reddish brown rocks; guanacos and a variety of birdlife; an excellent echo, got by shouting into a canyon and some (20m?) sandstone columns as sharply cut as anything I've seen made of basalt.