You can extract the RAR file with WinRar (Windows) or The Unarchiver (Mac)
You will get a UFS file that you can put in the following default locations:
Macintosh HD/Library/Application Support/UVISoundBanks (on Mac)
C:\Program Files\UVISoundBanks (on Windows)
After that your soundbank will appear in UVI Workstation's Soundbanks list.