The popular disk image management software like PowerISO, MagicISO, UltraISO are all fully capable of conversion of Virtual disk images (.vcd) to universal ISO disk images (.iso).
Unfortunately these utilities are not available for OS X. The alternative for Mac users would be to use some burning software, like Roxio Toast to burn .vcd disk image to blank CD/DVD-RW and create .ISO image from it with Disk Utility.
Also a Mac user could use some virtualization software like VirtualBox, Parallels Desktop etc. with virtualized Microsoft Windows to install any software listed below to perform this conversion.