You can find all the CAD Design Tools TI offers in the respective Product folder for each part. Example Click the link below for the product folder for the MSP430F157.
Scroll down the page for the heading Pricing/Packaging/CAD Design Tools/Samples.
Select the View link under Symbols for a list of symbols we offer for each package type.
I tried it on my MS 9 but it did not worked. However, Multisim does support Orcad design files -- extension ".dsn" -- which might be a workaround if you or someone has Orcad (or a demo version), you can open the symbol in Orcad and place it in your schematic, then save it as a ".dsn" file, and then open it from MS. Then you would select the component and do a 'save to database' operation.
Symbol files supported in MS have a ".sym" extension. However, in the symbol editor you can import pictures, bitmaps, ".dxf", etc. But in none of these I was able to open the ".olb" file you got.