I'm working in XNA but my problem is the math so I posted here.

FYI I am very new to this kind of math and I've been studying hard. I am to the point where I "think" I can solve this myself but once I try to work it out, I draw a blank.

Simply put, I am wanting sprites to oscillate (sine/cosine?) in a wave-like pattern along their vector. I've found several options that work with going along in a straight line along the X axis and I believe I understand how those work. However, my sprites aren't moving straight along the X axis and unfortunately I haven't found anything that is specific to what I'm after. Their vector can vary in basically any direction. What I don't know how to do is take the information from their vector and use it to create the oscillation I am after.

Any ideas?