I'm looking to purchase a modded xbox.. it has a matrix mod chip. Anyone know if those are good? Do those chips play PAL games? And do they have an XBL on/off switch?

it's old...
Unless you're getting a good deal on the premod - you might as well just buy a new premod with a newer chip installed.

http://xbox-scene.com/modchips3b_cheapmod_table.htm

And the chip isn't a deciding factor in whether or not it will play certain games - the bios that is on the chip is.

Well, it seems like a pretty good deal...

XBOX v 1.1 with a matrix xodus chip w/ an 80 GB seagate harddrive and two S-type MS controllers for $200 shipped.

would anyone happen to know if this can turn on/off for xbox live?

if you took a look at the link i posted you would see that your question is answered in the list.
Then there is also the installation guid on the same page which tells how to switch between modes on the chip w/ the onboard switches.

Try reading

Sorry, I was out when you posted that link so I just posted a quick reply when I got back.