Is it possible to allow some users to login to a server with ftp while limiting others to sftp?

I would like to allow most users to merely use ftp, cause they have the tools to use it and know how. But, some accounts are used only to transfer "sensitive" data and the owners of this data have asked if it is possible to force those particular users to use sftp. I think this is probably possible but I am not certain and wouldn't know how to go about setting that up.

I currently have both ftpd and sftpd running on this server, so that portion is done, now I would like to limit accounts.

Any ideas are greatly appreciated.

Thanks
Bob

You have to be specific.
Which ftp daemon are you using?

Yeah, sorry, didn't think about that till late last night. We are using "vsftpd" I looked through thier documentation a little but didn't see what I was looking for. Didn't see a whole lot on user permissions at all. The most I found was when they said to look at the man pages. I sent that to the folks who need it. But I am curious if anybody has done something like this.

Thanks