唔識英文?

第一，請搞清楚，有用already/yet/ever等字，不等於句子必須係 present perfect tense。
第二，有答題者話因為有 already ，所以就要用 present perfect，然後用 already 強調事情已完成。情況好似屋企有包發粉，所以要買個焗爐，咁就可以用到包發粉整蛋糕一樣。既然只係強調，咁其實冇左都唔影響意思架喎。
所以兩句中，I took a shower 其實已經可以。I had took a shower 就一定錯，因為有 had 就必然係 past perfect tense，句式係 had + past participle，o係呢句o既情況就會用 taken。

Absolutely, it very much depends on situation....

sometimes, "I took a shower already" is correct, especially spoken english

only need to use "simple past tense" to express the action had been done.

I took shower already OR I had a shower already

If you do this action everyday, you could say that "I take shower every day.
我每天都淋浴"。

I had took a shower already is correct.

'I took a shower already' is wrong because as you said 'already', you have to use present or past perfect tense to emphaize the completion of the task.

I had already taken a shower!

2007-05-28 22:56:20 補充：
THIS ONE BETTER I have taken a shower already.