Sentence structure

He has *good knowledge in computer language and good skills in using different computer systems to **finish his tasks thoroughly.
Firstly, with two changes * and **, your above sentence can be improved, keeping its original structure.
* is changed to 'a good knowledge of computer language' -- 'of' is a better preposition to use.
** is changed to 'complete' -- this gives a better meaning as you may finish a job and not complete it.
Your sentence becomes :
He has a good knowledge of computer language and good skills in using different computer systems to complete his tasks thoroughly.
The structure of the sentence can be changed further to give it a even better meaning, like this:
Having a good knowledge of computer language and good skills in using different computer systems, he always completes his tasks thoroughly.

2009-01-16 21:08:15 補充：
Typing error above:

'The structure of the sentence can be changed further to give it a even better ...'
should be
'The structure of the sentence can be changed further to give it an even better ...'.

2009-01-17 15:15:45 補充：
You asked: Should I keep "to finish his tasks thoroughly" at the end of the sentence ?
Yes, you should keep it at the end.

My suggestion:

With his good knowledge in computer language and good skills in using different computer systems, he is able to finish his tasks efficiently and effectively.