Before vb.net there was vb4, vb5, and vb6 for 32 bit windows programming. vb6 is going to stop being supported by microsoft early next year, and vb.net is the successor to vb6, so you should be using vb.net unless you have a good reason to use vb6.

vb.net has 3 versions, soon to be 4. vb.net, vb.net 2003, and vb.net 2005. You should use 2003 or 2005, but 2005 is better because it uses a newer version of the .net framework and has features that make coding easier.