I'm running 10.3.9 on my tangerine 300 mhz with 320 meg ram.
Works like a charm.
I have the 6 gb hd,with a custom install you can get OS-X down to 1.4 gig installed,then you can remove some languagefiles to win another 800 mb or so.
So yes,X will run,but a bigger HD would be better,even my 6 gig is a bit small if you want to run more apps then Mail and Safari,imho.