Have you looked at VMWare's free converter? http://www.vmware.com/products/converter/
It can convert various things to VMDK format, so if you can get your tib file in one of its supported input formats the converter will convert this to VDMK.
I used it to convert a version 10 tib file directly to VMDK format, but I don't think that the converter yet supports the newer tib file formats.