I would agree with other recommendations regarding "initial" MSL experience. SOS (Science Oriented Solutions) is a solid opportunity for entry level MSLs to gain initial experience. You might also want to consider MSL opportunities at a larger biotech or pharma company, where there is an established MSL program and sizable MSL team. This situation would potentially offer a slower transition, more training and would also most likely offer mentoring opportunities.
Relative to other MSL outsourcing programs, it may be hard to recommend venn5, since the company doesn't appear to exist any longer. Sources in the industry have confirmed that a former venn5 founder is back in the industry full time with Genentech. Seems like venn5 was phased out towards end of 2008. Can't confirm this, but after failing to contact the company directly or having any call backs the past 2-3 months during my search, not sure it exists. It was also a start up, so it may not be the right fit for first time MSLs.
Other companies to consider would be The Therapeutics Institute or Innovex. Both companies have MSLs and clinical or nurse educators.