Every few weeks they send home a new "book" which the child can keep, but it is really more like a pamphlet than a book.
In K, Open Court starts with a "pre-decodable" series. The words are simple, repetitive and closely match the pictures so the kids can make a good guess as to what word they need to "read" next. I believe that now we are doing a more difficult series, but I don't pay much attention since my daughter progressed way beyond it long ago. My preschooler seems to enjoy them very much, so at least someone in the family is getting something out of it ;)
If your daughter is already reading or close to it when she starts K, Open Court will be too easy. My sense is that it is a good system for teaching the slower readers, but if your daughter is more advanced, you and/or her teacher will need to supplement with more difficult material.
If you want to start with something similar over the summer at home to give her a head start, you can try the BOB series
http://www.amazon.com/Bob-Books-Set-1-Beginning-Readers/dp/0439845009/ref=sr_1_5/002-3177943-2173656?ie=UTF8&s=books&qid=1178931381&sr=1-5 or Brand New Readers
http://www.amazon.com/Brand-New-Readers-Green-Set/dp/076362599X/ref=pd_ybh_12/002-3177943-2173656?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=0XE0K1326BCJVVKW0TKV&pf_rd_t=1501&pf_rd_p=280800601&pf_rd_i=ybhThey are similar to the Open Court system. My daughter got a pack of Brand New Readers when she was four and she really enjoyed them.