I have both FS2004 and FSX. I'm curious if I can install FS2004 on one computer and connect via multiplayer to FSX. I don't want to do the fancy FSX multiplayer stuff, just basic "old-school" fly-togethers. Is that possible?(NOTE: I haven't tried multiplayer in FS since the 1980s, and never over TCPIP, so I'm not expecting anything fancy!)

This morning I tried getting FS2004 to multiplayer to FS2004. This worked fine. However, I couldn't get FSX and FS2004 to see each other.I noticed that FS2004 uses port 23456, and FSX uses ports 6112 - 6120 or so (I forget the exact numbers).Even when I tell FS2004 to use port 6112, it cannot see sessions hosted by FSX, or vice versa.So, is it impossible to get FS2004 and FSX to fly together?

I wouldn't say it's "impossible" but I would say it's not designed to do that. In fact, differing versions of FSX are not designed to be able to fly multiplayer together.For example, a person using RTM would not be able to join a session hosted by someone using FSX SP2.So, I think you're probably out of luck.

It can be done using FSHost (requires a small client program on FSX, but FS9 can connect directly). See http://www.chocolatesoftware.com/fshost/