What UNIX are you using? If it's SUN Solaris then there's SUNForum which is a free Netmeeting type app (compatible with NM too). Alternatively if it's not Solaris you might get some milage with RealVNC but I'm not sure it will support the graphics required by V4. Other applications like Hummingbird Exceed are also available.
Using Netmeeting it's going to be very very slow and probably unuseable even on an 100Mbs LAN.
All I can tell you is that we use Netmeeting on AIX and IRIX with CATIA V4 and it seems to work well. I do not know the code levels or the protocols being used. I didn't set it up.