Hi and welcome to the forum
any Ef lens will fit on all of the EOS line of SLR's. Ef-s lenses will not mount on FF cameras such as the 5D, 1D/Ds and can only be mounted on APS-C cameras
In short as long as you buy EF lenses you will be able to mount them on any canon DSLR.
You just have to be careful of one thing, you will get a smaller Field of View with your 450D then on a 5D
the 85mm will give you the same Field of view as a 136mm lens on a 5D (85mm x 1.6(crop factor))
hope this answers your question