Can a PAL xbox 360 get an update to run NTSC games on it?

nope cant be done - you would need to buy a NTSC one from america or something like that

Some NTSC games may play on a PAL console, depends on the game and the game's publisher.

PAL consoles play NTSC games just fine...as long as they are region-free. PAL/NTSC is generally meaningless these days, anyway, since most games run at 60hz as it is.

What I think you're actually asking is: Can the Xbox be updated to play region-free games?

The short answer is: NO.

The long answer will get you banned.

MOST games will play NTSC games. Always check before buying though Skyrim comes to mind as a region locked game.

I have the US version of MW3 that I picked up before the release date from Dungeon Crawl in Melbourne for $60. It's NTSC and runs fine on my PAL console. I've received all title updates since launch automatically.  And my "Aussie" purchased Elite account syncs just fine as well.  If the game is region free, it's not an issue to receive updates etc. If it's region locked, well you're not even going to be able to load the disc up, let alone worry about title updates...

As the poster above said, PAL & NTSC is pretty much meaningless in the HD world now. The game will either run at 720P or 1080P and 50-60Hz isn't an issue also if you have a TV that was bought within the last 5 years...