How can I make alpha transparent AVI file

[MI6]

I have several AVI flourish video clips in AVI format with solid black background.When I import them in Vegas and adjusting "premult. dirty mode"in properties (like I used to do with other alpha clips) I can't get transparent (overlay) effect.
Media is 720x576x32bit.Any suggestion how to use these video clips?
Regards.

[poisondeathray]

Need more information. What kind of AVI? What compression? Is there embedded alpha or dummy alpha? Is there a separate matte clip (white & black) ?

What do you mean by "flourish" . What is supposed to be overlayed on what ?

[MI6]

I have download these files from torrent, for use in After Effect as part in AE project file, so I don't know more information about files.

[poisondeathray]

That doesn't help. It can be a number of things. You need to provide the information requested or upload a sample clip

If there is embedded alpha, then you right click the clip and under the media tab, alpha channel, select one of the options. Usually straight is safe to start with

[Cornucopia]

I agree with pdr, but want to add:
Just because there is an alpha channel doesn't mean it has anything in it. Without anything in it, it acts just as if it were a 24bit file. If you have black as a background (but NOT as a a foreground element) and no true alpha, you can avoid the alpha stuff altogether and just use a Luma Key effect.

BTW, if you're going to be using AE, why the bit about Vegas in the OP?

Scott