「は」「が」「を」with 「〜たい」

新聞が読みたいです: I want to read just a newspaper.
新聞を読みたいです: I want to read a newspaper.
その新聞はとてもおもしろいそうだ: The newspaper is said to be very interesting.
その新聞は読みたい:The newspaper wants to read .... is not correct.

Sorry, my poor English.

新聞が読みたい
新聞を読みたい
どちらも同じ意味ですが、個人的に新聞が読みたい、のほうを良く使います。
新聞は読みたい、間違えです

新聞が読みたい
新聞を読みたい
　→かなり近い表現で、日本人でも違いを探すのに困るくらい。

新聞は読みたい
　→「雑誌は読みたくないけど新聞は読みたい」というニュアンス。「新聞は読みたい」とだけ言うと、「じゃあ何は読みたくないの？」と必ず聞き返されます。

新聞を読みたいですand　新聞が読みたいですare the same means.
新聞は読みたいです　is wrong phrase.
This sentence means "Paper want to read."

私は新聞が読みたいです　is correct sentence.
その新聞はとてもおもしろいそうだ。　is correct sentence.
その新聞は読みたい　is not correct.
その新聞を読みたい　is correct.

日本語はてにをはで、ニュアンスが微妙に違うので、難しいですよね。

私は新聞を読みたい＝私は新聞が読みたい
どちらも同じように使えます。

新聞は読みたい、とはあまり言いませんね。
あえて使うなら、「新聞は読みたい。でも他のことはしたくない。or（でも他の雑誌とかは読みたくない）」といった感じで使えます。
「新聞は」というと、新聞だけと限定するような感じですね。

新聞が読みたい
It is the shorting of “A newspaper is what I want to read.”

新聞を読みたい
It is the shorting of “As for me, I am in the condition that a human (or I) wants to read a newspaper.”

See
http://lang-8.com/satoshi/journals/828534/

I think that を読みたい and が読みたい are used in different situations. For example,

What do you want to do now?
(今、何をしたいの？)
― I want to read a newspaper.
(新聞を読みたいな。)

Which do you want to read, a newspaper, or a magazine?
(新聞と雑誌、どっちが読みたいの？)
― I want to read the newspaper.
(新聞が読みたいな。)

But, as another answerer mentioned, some Japanese use both が and を in the first situation. On the other hand, it's awkward to use 新聞を読みたい in the second situation.

And I think that 新聞は読みたい itself is ungrammatical, but the 新聞は読みたい used in the situation which you mention can be used, and the expression implies that B seldom reads newspapers.
And I also think it's more natural to add だけ, like その新聞だけは読みたいな。

will try to answer your questions.

First of all, I will answer your first question: the difference between 「新聞を読みたいです」 and 「新聞が読みたいです」.

「新聞を読みたいです」 means that a speaker wants to read a newspaper. This is a normal sentence. Generally, 「を」reveals the meaning of objective cases.
「新聞が読みたいです」also means that a speaker wants to read a newspaper. But, in this sentence, the speaker is emphasising the word "a newspaper" by using not「を」but「が」. In other words, he/she is implying that he/she wants to read not a book, a magazine, but "a newspaper". As a result, in this sentence,「が」demonstrates the implication of emphasis.

Next question: whether「新聞は読みたいです」can be used if the newspaper is the topic of the conversation.

Sorry, I could not understand the definition of "the topic of the conversation". Do you mean that the topic of the conversation is a subject in a sentence?

The answer of whether「新聞は読みたいです」can be used is depending on situations. Bacially, the sentence has two meanings. Native speakers of Japanese can judge from the flow of conversations which meaning the sentense shows.
One of the meanings is that a speaker wants to read "a newspaper" though he/she does not want to read anything to read except newspapers. In short,「は」means "only". In this case, 「新聞は読みたいです」is a correct sentence.
The other meaning is that a newspaper wants to read. In this case, 「は」demonstrates that the newspaper is the subject of the sentense. As you know, in this sentense, if the subject is a newspaper, the meaning is a little bit strange because normally, newspapers do not read anything to read because they are not human beings. For example, books do not run because they don't human beings though in imaginary stories such as "Alice in Wonderland", books might be able to run, walk, or talk...hahaha...
As a resut, in this case,「新聞は読みたいです」is an incorrect sentence.


Last Question:

A: その新聞はとてもおもしろいそうだ。
(It is said that the newspaper is very interesting.)

This sentense is correct.


B: その新聞は読みたい
(Two meanings: ①A speaker wants to read the newspaper though he/she does not want to read anything to read except the newspaper. ②The newspaper wants to read.)

①→correct
②→incorrect

Good luck in your Japanese study!(^^)!
Kitty

新聞「は」読みたい　＝　新聞以外（の何か）は読みたくない
新聞「が・を」読みたい　＝　新聞を・が読みたいという願望

Thank you all for your replies, I greatly appreciate it.