Although Niger's natural beauty and desert landscape make it a geographically appealing location, the violence and fighting that plague many regions of the country make it somewhat less appealing for the casual traveler looking for a safari. Traveling to Niger is not recommended, although it's not the most dangerous place in Africa and it's not like you need to be accompanied by UN troops or anything.
What to do
There is plenty to see, but the best way to have a vacation in Niger would be to spend your time offering relief and volunteering in areas that have been affected by drought. Not only will help some people, but you'll meet locals and interact in a way that is impossible as a traveler. And I'll bet the locals know the really beautiful sights and places to see.
You can also drive from neighboring countries to the capital city Niamey, or cross the Sahara on foot to get into Niger, although only the reckless choose that route.
Where to stay
There are hotels in Niamey that can set you up in the highest luxury, although your view of the country may be heavily biased. For a more realistic experience, there are guesthouses and hostels for tourists, or, as mentioned above, try volunteering in an afflicted region.
There is more information about Niger on the message boards where you can ask questions and get personal responses from travelers that have been here. Also, read the wild and weird travel stories by folks who have been to Niger and came back (in one piece) with a story to tell.