隔てる

Examples from WWWJDIC:

# 日本海は日本とアジア大陸を隔てている。 [T]
The Japan Sea separates Japan from the Asian Continent.
# 彼は私たちと道を隔てた反対側に住んでいます。 [T]
He lives across the street from us.

My problem is with the second sentence. In the first sentence wo marks what is being separated, while in the second it marks what things are being separated with. I don't understand why this is, can anyone help?

Hmmm, it really is difficult to explain even in Japanese...

隔てる means (1) there's something (or space), or (2) to place something, to prevent the direct contact etc. between the two.
# 日本海は日本とアジア大陸を隔てている。 [T]
The Japan Sea separates Japan from the Asian Continent.
Alternatively we can say
日本とアジア大陸は日本海で/日本海によって隔てられている。
This fits the above (1), Japan Sea lies between Japan and the Asian Continent. (So Japan and the Asian Continent are separated.)
# 彼は私たちと道を隔てた反対側に住んでいます。 [T]
He lives across the street from us.
And this is an example for (2), we might say
He lives on the other side putting the street between us (= he and ourselves).
I hope this helps a little.

That helps、Thanks