“NEW” script

I’m trying to make a script that will check if there’s been a new post in a category in the current day or last day, and if so, do something like display a “new” icon, or bold a link.

All I could find to work with was get_lastpostdate() and unfortunately I’m not a php guru. I figure I’ll need to compare the last post date with the current date, and if they’re the same or close to same (to the day) then do the action (icon or bolding).

So things I need to know:
-How to find the last post date of a specific category or group of categories.
-How to get the current date.
-How to chop the last post date and current date to just the YMD format, NOT including time.

Thanks.