VLC Streamer uses VLC to handle the actual conversion of movies to the format for the iPhone/iPad.
If you're using Windows XP, you should definitly upgrade! However, if you won't or can't, then the last version which officially works on windows XP is version 5.10
If you are using an old version of Mac OS (Mac OS 10.5, or Mac OS 10.6 on a 32bit CPU), then please use version 3.50
If you're using Mac OS 10.6 on a 64bit CPU, then the latest version you can use is version 3.91
The linux version is unsupported. It was provided by a generous community member. More info here.
The A version is based on the current VLC. It is best for most filetypes.