The PSAT
The PSAT is the preliminary SAT which will be offered at most schools on October 21st in 2006. It is essentially the same test as the SAT with fewer sections and no essay. The PSAT is tied to the National Merit Scholarship Corporation which awards 17,000 students the status of National Merit Finalists. About half of these students receive scholarships. The test must be taken by the 3rd year of high school (11th grade) and you must confirm your success on the PSAT with a comparable score on the SAT. The PSAT must be signed up through your high school and is most likely administered there. The October 15, 2005 PSAT has been published and should be available through your high school's guidance/career department. The test is also available here.
The PLAN Assessment
Essentially the pre-ACT. This test is for 10th graders who want to get a feel for the ACT. As far as I know, it doesn’t have any scholarship money associated with it. Like the PSAT, the PLAN is offered through high school and will most likely be administered there.
The idea behind PSAT/PLAN
Preliminary
examinations are meant to show students both the type of
questions to expect and the testing conditions they will
experience on test day. The tests are relatively student-friendly
in the sense that they are not full-length examinations.
They are meant as a transition and ease a student into the
world of formalized test-taking. Another reason to take
a preliminary test is to get a score that "colleges won't
see." The test scores from these preliminary examinations
are not directly sent to colleges unless you give permission.
However, most high schools will place the scores on the
high school transcript, and you may request for them to
remove it. This actually holds true for the ACT and SAT
as well. Some students may take both tests but only send
their scores from one. The guidance department at most high
schools will receive both scores and append the scoring
labels from both tests onto the transcript. Although a student
is trying to hide his scores from one test, most colleges
will still see both scores.