has a good vector library which should more than suit your needs and there's also many other vector math libraries for free too. As well as Eigen
which seems very simple to use.
Boost comes with a lot of other libraries that you may find useful as you go along.
I was looking for a download link to another library just for the vector math for another one, SVL, but couldn't find it.
EDIT: Whoops, I guess you're using Pure Basic instead of C++... Doh
Mental arithmetic? Me? (That's for computers) I can't subtract a fart from a plate of beans!
Warning! May contain Nuts!