Another option that we use successfully is purchase a GlobalMapper license (~ $600) and you can convert .SID to the formats that TBC 5.51 supports - GeoTiff, .JPG/.JPW (not JP2), .ECW/.EWW files. GlobalMapper allows you to not only convert image type and decompress MrSid raster files, but very quickly change coordinate systems of geospaital data (CAD, LiDAR data, Imagery) to the coordinate system of your TBC project. And units as well. Well worth the small fee to have it and it can handle very large datasets, very quickly.
------------------------------
Ben Sullivan
------------------------------