Android 3.x (Honeycomb) is not officially available for the original 7" Samsung Galaxy Tab tablet. Furthermore, since the source code for Honeycomb was not made available by Google until very recently (as part of 4.0/"Ice Cream Sandwich" release,) any currently existing 3rd-party custom ROMs were built against the SDK (Software Development Kit,) and are therefore missing critical features such as GPU acceleration, for example.
You can still try Honeycomb SDK-based custom ROMs that are available on sites such as XDA-Developers or Rootzwiki, although most ROMs will be based on Gingerbread (Android 2.3.x) since it actually was open-sourced by Google for a while now, and some Galaxy Tab variants actually received an official 2.3 upgrade from Samsung.