I would like to know if there is a website where I could download the Apache POI ported for .net?
I already found this link in the web http://www.apache.org/~avik/di
I found out the answer. You can get the latest apache poi version then convert the jar into dll on your own using IKVM.NET. After that, add the assembly of the POI dll to your .net application plus the IKVM.NET core and JVM dll. And you can finally use the Apache POI in your .NET project.
Another solution is a partial port of POI to .NET, named NPOI.
(Found it on that other question)