a)In case you want to restrict the posts of one specific category, look at its ID_CAT value in table [smfprefix]_categories and write it down.
- backup any file you are about to modify before doing so

-In mod_smf_recenttopics(i tested it on 2.0) where it says:
WHERE t.ID_LAST_MSG >= " . ($modSettings['maxMsgID'] - 35 * min($int_num_topics, 5)) . "
change it to:
WHERE b.ID_CAT = thecategorynumberyouwrotedown
AND t.ID_LAST_MSG >= " . ($modSettings['maxMsgID'] - 35 * min($int_num_topics, 5)) . "
b) If you want to show post of a specific board, donīt do the former modification. Just look for the ID_BOARD value in the [smfprefix]_boards and write it down.
- backup any file you are about to modify before doing so

-In mod_smf_recenttopics(i tested it on 2.0) where it says:
WHERE t.ID_LAST_MSG >= " . ($modSettings['maxMsgID'] - 35 * min($int_num_topics, 5)) . "
change it to:
WHERE b.ID_BOARD = theboardnumberyouwrotedown
AND t.ID_LAST_MSG >= " . ($modSettings['maxMsgID'] - 35 * min($int_num_topics, 5)) . "
I find this can be specially helpful if you are running a bilingual site and have a separate forum category for each language. Then, you can guess what else you have to do to display the latest topics in the forum in the language chosen by the user

Note to Wolverine: It would be very cool to be able to have this as 2 parameters in the moduleīs backend

Cheers,
NiCo