Hi
Some first names, places and dates would be helpful

If you go onto the National Archives site (
http://www.nationalarchives.gov.uk/ ) and enter "Malecki" in the search box at the top right hand side, there are 19 results, mainly applications for naturalisation in the UK.
Naturalisation records are useful as they usually give dates and places of birth, occupations, children's names and ages, and parents' names.
Do you mean Opatówek near Kalisz?
http://www.rootschat.com/links/0rdq/ http://www.rootschat.com/links/0rdr/give the LDS (Mormon Latter Day Saints filmed lots of parish registers all round the world and make them available at their centres) Catholic BMD film holdings for Opatówek.
If it is this one, then it falls within the Poznan Project area -
http://poznan-project.psnc.pl/ - and you may be able to find marriages of your ancestors on this site. I suggest you use the Extended Search section and put the surname in the Groom's box then select the region that includes Kalisz.
Or is it Opatowiec, Pińczów, south of Kielce, at one time part of the Russian empire?
The list of LDS films for Opatowiec are here:
http://www.rootschat.com/links/0rdu/Gaie