Slightly old topic but I think this is useful, to answer my own question a little.
Caffler wrote: as for that le n-ól vs le h-ól/le hól,
le n-ól when le is used in the same sense as chun - "in order to"
le h-ól when the meaning is to be drunk
táim anseo le n-ól - i'm here to drink
tá bainne le hól - there is milk to be drunk
anyway that's just my take on it and someone will probably pick it full of holes

I found a little more data on this and thought I'd share...
Let's examine some of the examples provided on page 115 of "Progress in Irish":
rud éigin le n-ithe (something "to eat")
rud éigin le n-ól (something "to drink")
The construction "le" + verbal noun describes a purpose for the "something" that has yet to occur. It may make things clearer if we translate the above examples as though the verbal noun is a "passive infinitive" instead of the infinitive used in the book, i.e. "something to be eaten" and "something to be drunk" instead of "to eat" and "to drink".
Source:
http://groups.yahoo.com/group/progressi ... ssage/1763So:
táim anseo le n-ól =
i'm here to drink in terms of the above -- "I'm here to be drinking something" (not yet occured)
tá bainne le hól =
there is milk to be drunk which is a statement rather than a "passive infinitive.
Any thoughts?