There doesn't seem to be much around for Windows 7 EQ, if there isn't one included with the sound device and there isn't with the sound device you have in the PC.
Some media players, such as the Windows Media Player have built in EQ options, but they are only applicable when you are using the media player.
Doing a google search, this is a common complaint with Win 7. My suggestion is to get some different speakers that have a tone control on them. Those Bose speakers have the Bose name but are not the best speakers Dell sold with new PC's. Get a standard "Analog" 2.1 speaker system and connect them to the GREEN speaker jack on the rear of the PC, not a USB connected speaker set. You can get PC speakers at many places, you don't need "Dell" speakers.