We all know that while AutoCAD uses blocks, MicroStation uses cells. The names are different but the concepts are relatively the same. Unfortunately, the way in which blocks and cells are saved are completely different in AutoCAD vs. MicroStation.
In MicroStation, cell libraries are saved as .cel files and are created and stored in MicroStation as a several models within a single file. This way, 1000 cells can all be accessed via a single file. In AutoCAD, each drawing only has one drawing surface (what MicroStation users would call a model) and is therefore unable to hold all of the cells in the same way MicroStation holds them.
A "block library" can be one of two things. It is either a directory in your machine where a lot of dwg's are stored or a single dwg has the blocks placed inside the drawing itself, all sharing the workspace. This second kind of block library is what we will be working with here.
How do we turn a .cel library into an AutoCAD "block library" in which the blocks exist together in a single drawing file?
1. Download the CellUtils.ma utility from the Bentley Communities File Page
For MicroStation V8i: http://communities.bentley.com/communities/other_communities/bentley_library/m/bentley_library_utilities/174156
For MicroStation V8: http://communities.bentley.com/other/old_site_image_galleries/member_folders/m/phil_chouinard_bentleys_files/186
2. Follow the instructions for downloading the cellutils.ma utility: http://communities.bentley.com/communities/other_communities/bentley_library/w/bentley_library__wiki/cell-utility.
3. Open a brand new, blank MicroStation file.
4. Load the cellutil.ma and use it to create the grid of cells you want to be included in the library.
5. Choose Element Selection tool. In tool settings, extend settings window. Choose tab 'Element Type'.
6. In the 'Element Type' tab, choose 'Text'. Once chosen, deselect any Element Type that isn't 'Text'. (When you choose 'Text', the Element Select tool selects all text elements. If any of your cells happen to have text in them, deselecting 'Annotation Cell' will deselect those cells but keep the text of the descriptions).
7. Choose Delete Element tool. All text in file is now deleted and the cells lose their description and time stamps. Highlight all elements that make up the grid created by cellutil.ma and delete them until the only elements left are cells.
8. Go to File>Save As... and save the file as a DWG. The file is now a "block library" ready to be opened in AutoCAD.