If you want to create custom pois and use it with your device (the device should support custom pois in a gpi format) you should use the tool Garmin POI Loader (or Garmin Content Toolkit. CT is for locked POIs and has a few functions more than POI Loader). POI Loader accepts csv and gpx for creating gpi custom POIs and bmp for the image of the poi. You can use GPS Babel for converting the data stored in the xls file to gpx/csv and create a gpi file with POI Loader.

I think if you just put name over the columns in Excel lets say - Latitude, Longitude, Name, Address etc. that will be fine for the convertion with GPS Babel. (Sorry I am lazy but if you have troubles with this explanation I can provide you example later but I really don't find it so hard)

If you want to create a garmin POI image map you should look at the section for creating Garmin IMG Maps for further instructions. (At the moment I can't think what would be the advantage of creating Garmin POI IMG map compared to Custom gpi file with POI Loader but this mainly depends from your device.)

So...what is your device and what is the purpose of the task?