picked up an 06 klx250s today with 78 miles, could never get it to run, the engine turns over, and though difficult you can occasionally catch a moment of the bike running for about 1 second, then dying again. the bike is in amazing cosmetic condition, owner said it never went over 45mph, so that's the worst that could be wrong with it?

 

You have an '06 with only 78 miles?!? Wow! Nice find. Welcome to KF.
From what you describe, I'd be looking to the fuel system first. Plugged carb jets, fuel not getting from tank to carb, etc.

You'll get more input posting in the KLX250 specific forum: KLX 250S - Kawasaki Forums