I don't know if I can purchase both CS5 and LR3 Student Teacher Editions together. The restrictions with Student Teacher editions say you can only purchase one license of any Adobe STE product within a twelve month period. Does this mean I could purchase CS5 now and in a year buy LR3 or it's newest version?
Yes, you can buy both now, or whenever you want.
Per Adobe's Student Edition FAQ, "Each eligible person may purchase only one copy per Adobe Student and Teacher Edition title ..."
However, those two products are different titles - so you could get a copy of each. There's an example of how it works given in the FAQ.
It's a good thing actually because you probably will never have an opportunity to get a better offer on Adobe products than when you're a student.