What is the process to bring a relative here for a visit ? My wfe wants to bring her little sister here for a visit , my wife is from Colombia and her sister still resides there . Is it possible for her to get a tourist visa or can i apply for some type of visa for her , being responsible for her return ?
thanks

Her sister would need to apply for a tourist visa on her own, there is no visa where you are responsible for her return. You can include a letter of invitation, detailing the visit, but she needs to have very strong ties to Colombia, such as a job, any property she owns/rents - things showing she is likely to return to her country. She also needs to be able to show sufficient funds to support herself while visiting, as far as I know.
Young, single women from South America are rarely granted tourist visas, but if she can show certain things, it is possible. Colombia isn't one of the highest denied countries with a denial rate of 33.3% in FY 2006, but it isn't one of the lowest either.

http://travel.state.gov/visa/temp/types/types_1262.html#3