Can .AVI & .MPG/.MPEG files be played on DVD players?
 

I seriously need to know, because I'm getting some things for my cousin burned on to DVD.

I burned a DVD with both file types on them a couple months ago (can't remember what program I used), they all seem to play fine.

Not unless it is a DivX compatible player. So if it isn't you'd have to convert the files to either VCD or SVCD format (and then burn them on cds) to be able to watch them.

What about Quick Time or RealPlayer applications?

only Avi with Divx codec play on compatible DVD player compatible.if you have it

I've converted avi's to mpg's using TMPGEnc, and they've played on my old school dvd player just fine.

Since both formats hardly work anywhere else outside of their programs, you'll have much less luck playing these files on a DVD player than DivX, XviD or most other formats.
You'll have to find some way to convert the QuickTime and Real files to mpeg2, then put them in a DVD like format for them to play on a DVD player.