As far as i understand, condition zero is just a revamp of the current counter-strike (with single player etc..) so i would imagen it would work, although i wouldn't rely too deeply on my word. If you want ESF working, you'd be best off just going and buying "Halflife Game Of The Year Edition". Cheaper, its already out and we know that it'l definitly run esf. Counter-strike is a mod which you can download for free anyway.