Foreign investors are welcome in Niger.
Company registration is easy, you need a sollicitor, not a lawyer, 1500€ and a couple of hours. The whole process takes 2 weeks, as Harishv said.
Note that Niger is part of OHADA agreement, thus business laws are more or less the same as in Ivory Coast, Senegal etc... Only a little less efficient.
About recruitment... Niger is a cool country, people are nice, halas most of them are illiterate. A lot of internal training/skills acquisition is required. Unemployment is endemic, expect hundreds of CV's if you put an ad in local newspapers. (I personnally beat the record with more than 5000 CV for 75 positions... Had to retain a HR consulting firm to process them all)
The biggest problem when it comes to business in Niger is that the country is landlocked, thus everything is to be imported, mainly from Ivory Coast, Benin, Togo and Nigeria.
Should anybody need more advices => MP me!