下列兩句的意思是否分別不大？

The first sentence is wrong in grammar, while the second is correct.

Past perfect tense is used to indicate that one event or action occurred before the other in the past.

Rewrite the first sentence with past perfect:
I had finished my work in the garden before Sue arrived, so I could welcome her at the door.

2012-08-19 12:03:53 補充：
First, it is kind of strange to use continuous tense on "finish", although I have no evidence to say it is wrong. To choose the verb "do" would be more natural.
Now, the discussion is focused on the difference between past perfect continuous and past continuous.

2012-08-19 12:07:35 補充：
Rewrite the first sentence with past perfect continuous: (use "do" instead of "finish")
I had been doing some work in the garden for three hours when Sue arrived, so I didn't hear her come in.

2012-08-19 12:25:59 補充：
past continuous:
at some point in the past (when Sue arrived), an action ("do") was in progress.
past perfect continuous:
at some point in the past, an action had already started before that and was in progress. (3 hours before Sue arrived)

AhShing 很多謝你的回答，但我不同意你的回答。

我認為第一句是正確的。

2012-08-18 21:00:43 補充：
因為 I had been finishing some work in the garden when Sue arrived 這部分有兩個動作，分別是 I had been finishing some work in the garden 和 when Sue arrived ，而 I had been finishing some work in the garden 發生在 when Sue arrived 之前，

2012-08-18 21:00:48 補充：
所以這正符合你說的 ：Past perfect tense is used to indicate that one event or action occurred before the other in the past.

2012-08-20 16:16:10 補充：
第一句有兩個意思，第一，some work in the garden剛剛結束；第二，some work in the garden 仍進行。

第二句只得一個意思：some work in the garden 仍進行。