How do the homologous chromosomes pair up and position themselves along the center of the cell?
There are many things involved in the pairing of homologue chromosomes. 

Before mitosis can occur an important prerequisite must happen: the division of centrosome. This small complex is the principal microtubule-organizing center in the (animal and therefore human) cells. During interphase the microtubules originating from the centrosome, project to the cell perimiter with their + ends (this where they grow). At the beginning of mitosis the duplicated centrosomes separate and migrate to oppsite sites of the nucleus to form the poles of the mitotic spindle. As the nuclear envelope disintegrates the spindle captures the chromosomes at the cetromeres. Since the microtubules are growing from the centrosomes this capture eventually pushes the choromosomes to center. Source: The Molecular Biology of the cell. Fourth Edition. ISBN: 0-8153-3218-1 (hardbound) 0-8153-4072-9 - (pbk).
A searchable online version: http://www.ncbi.nlm.nih.gov/books/NBK21054/

I've found a few good articles with many details:

Current Biology, Volume 12, Issue 17, 3 September 2002, Pages 1473–1483
The Dynamics of Homologous Chromosome Pairing during Male Drosophila Meiosis
Julio Vazquez, Andrew S Belmont, John W Sedat

and 
Homologous pairing and chromosome dynamics in meiosis and mitosis
Bruce D. McKee

I took a quick glance at the above mentioned articles, and it seems that homologous chromosomes tend to be close together (paired if you wish) during interphase most of the time.