Searching DT by date modified or date added

As part of my research, each day I load new RSS feeds and emails into DT. Once a week, I then need to search ONLY the past 7 days for specific keywords. I don’t know of anyway to do this. Anyone have any ideas?

Is there a search parameter I can use?
e.g., searchterm and date.modified within or between date X and date Y?

I also need to group items by date. Like week of 8/1/2010-8/7/2010, then week of 8/8/2010-8/15/2010 etc…

Pending the probable future introduction of date ranges in smart groups/Advanced search button, I select items that fall within a date range by adding the desired Date column (Added, Creation, Modification) to a view window or, for database-wide flat few of contents, to the History window (Tools > History). Sort by date and select the desired items.

Of course, there’s an existing smart group for Today, and Christian has noted tips for adapting this to several other ranges.