HI Brenda

I think a course could be a really useful tool - but it all depends on your learning style. We've learned all of the Adobe CS3 programs through self teaching, tutorials provided with the program online, and books - but that was out of necessity (you see, there simply weren't any classes available in the far corners of the world we were living in.)
You can certainly learn a lot about the programs without a course, but Lisa is right in that Photoshop alone is a complicated program - having someone in a classroom setting to help guide you would only benefit you.
As to which program to purchase - we went ahead and bought the whole kit (the $1,800 was tax deductible as a business expense

) but we use things like Dreamweaver and Illustrator on a regular basis. And of course nothing beats Adobe's PDF maker.
You can download free trial versions of almost all of the programs included in CS3 - they're not full featured, but might help you determine if you need the whole suite or just part and parcel.