Strengths/Capabilities Various Languages

We are converting from an IBM Midrange AS/400 (using DB2, OS/400, RPG/ILE) platform to a MS SQL 2000 server based ERP software. What language training do my programmers need? What training does my network admin need? Do Visual Basic, C++, and Java all do the same thing? Do they need to know all of them? or?

The primary need will be for developing programs accessing the vendor supplied files and developing supplemental applications – limited web interface.