I am new to JSF. I have some working custom JSP tags which I want to use in JSF xhtml. Is there any way to do that? Any pointers will be appreciated.
I don't think you would even want to. The first thing I'd do is check out of extension frameworks like Icefaces, Tomahawk or Primefaces don't already provide components that do what you want. If there is really no other way, I'd research into creating the custom tags/components "the facelets way" (facelets is the "xhtml" you speak of, better stick to the proper terminology if you want to ask clear questions).
And don't ask how to create facelets components, that is the territory of a good book.