(This is not meant to be a competing answer, but there are not allowed enough of these precious characters in the comment line.)

The Finnish text may be difficult to translate into English and it is awkward in Finnish also. The meaning of it is clear, though, and can be expressed like that: "The company's line of business is that it manufactures (?) wall and floor coverings and other ... by itself and by/through/in collaboration with its affiliates and its shareholding companies.”

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Note added at 4 hrs (2006-09-01 17:51:46 GMT)
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I got an email about Anu's response and took again a look at the question. First, my translation might be better as "...line of business is manufacturing...", but that's not why I am writing this.

I stopped pondering why the Finnish sentence is awkward. The reason is that 'itse' is usually after the verb when meaning 'by oneself': "Yhtiö valmistaa työkalut itse", "Hän huoltaa autonsa itse". 'Itse' has many meanings and when it is near the subject of the sentence its meaning is often 'oneself', 'in person': "Rehtori itse (arch) / Itse rehtori saapui" (The rector himself / in person arrived)

The orginal sentence would be more natural if it were arranged like that: "Yhtiön toimialana on seinä- ja lattiapäällysteiden sekä muiden lattiamateriaalien valmistaminen (?) sekä itse että tytäryhtiödensä ja osakkuusyhtiödensä välityksellä..."

So, the awkwardness in the original sentence lies in that 'itse' meaning 'by oneself' is move far away from where it usaly is (after verb/predicate = 'valmistaa/valmistaminen itse')

Of course, I don't know what follows in the original sentence. Maybe there haven't been other possibilities to arrange the sentence than the one used.


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Note added at 20 hrs (2006-09-02 10:03:52 GMT) Post-grading
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Thanks Elena! I am much appreciated by your kind words.

Two additional notes:

There's a typo in Finnish text. Gen. pl. of 'yhtiö' is 'yhtiöIden', not 'yhtiöden' as it stands there now.

'Sen (i.e. yhtiön) osakkuusyhtiöt' refers here to the companies that (together) own the company concerned.