[greencreeper]

The MCDST is specifically a Windows XP qualification, rather than a generic IT qualification. There are two exams - XP itself, and XP and applications. If you already use XP, then I would say buy a book and self-learn - the courses (pricey) aren't going to teach you much more. When I sat the exams they were about £90 each. If you want a generic IT qualification, maybe something like the A+ would be more appropriate?

Practice exams and materials - do a Google for "braindump". The first couple of links should have a range of questions/answers supposedly taken from the exams (you'll probably need the exam code, which you can get from the MS website link that Jon posted above).