Doing vasudan voice isn't as hard as you might think.
The actually supposed 'language' they speak can be a pain to replicate sometimes, but in which case you just use extracts from the solo-vasudan voice sample.
All you need do is record what you want saying an run it though a few filters to get the desired distortion and such. Then fade in some vasudan speech effects into the background and you have yourself a working vas-voice.
But of course to actually do decent vasudan speech you will more than likely need a good quality sound editorial program such as sound forge. It doesn't have to be a top of the line professional program, but you will need a quality program to get the job done. There are free downloadable programs that you could use, but I couldn't tell you where to look since I don't know.