Poiloader does not support .xls only .csv which can be created with Excel.
GPX is the most powerful format of course .csv is very limited.
Here's the writeup from Poiloader help.
Creating .CSV Files
POI Loader accepts .csv files that contain longitude, latitude, speed alert information, and optional comments. You can create .csv files using a text editor, MS Excel, or a similar program.
POI Loader assumes a .csv file utilizes the following format for each POI (brackets [ ] denote optional text):
<Lon>,<Lat>,["]<Name>[@<Alert Speed>]["],["] [comment]["]
Longitude and latitude must appear in WGS84 decimal degrees format (ddd.ddddd; negative numbers indicate West and South).
If you include quotes around the name or comment, you can include line breaks in the text.
The following are examples of Custom POIs in the proper format:
-94.74240,38.81952,Heritage Park,Perfect site for a picnic
-94.76416,38.81227,Garmin,"1200 E. 151st Street
Speed information can be included in the file name and in the name of individual POIs. See Understanding Speed and Proximity Alert Information and Creating Custom POI Files for more information.