I do not believe the 8100 has GPS built in so in order to use GPA and map applications, you will need a GPS puck to receive the signals.
Also, the Pearl has limited internal memory so your install of the map application and themes might be bumping against that internal limit. In addition, you cannot install applications to the SD card, only music, ringtones and photos.
As mentioned above, if this is a BB on the corporate BES, then the company IT policy might also be preventing 3rd party software installation. You will need to talk to the BES Admin if you are indeed on the BES.
As for themes, they are device specific. Are the ones you downloaded and installed specifically for the 8100?