DAT can be MANY things.
http://filext.com/alphalist.php?extstart=%5ED
DAT Nascar Racing Archive
DAT Unfinished FastTrack Download
DAT Nero CD Speed Results File (Nero AG)
DAT SPOT Graphic
DAT SHARP MZ-series Emulator RAM-Disk File
DAT RDXR020305.DAT is Morpheus Adware
DAT Novell Message File
DAT Terrasoft Dataset Definition File
DAT Runtime Software Disk Image (Runtime Software)
DAT Shareaza Thumbnail (Shareaza Development Team)
DAT SeeYou Waypoint (Naviter)
DAT Peachtext List Manager (Peachtree Software (Sage Software SB, Inc.))
DAT Chuzzle Saved Game
DAT LithTech Game Compiled Level File (Touchdown Entertainment, Inc.)
DAT My Personal Programmer Distributed Project (M:Pact Technologies)
DAT VMS Data File
DAT WordPerfect Merge Data (Corel Corporation)
DAT Z80 Spectrum Emulator Snap/File Format
DAT MS Word for DOS File
DAT Windows Registry Hive (Microsoft Corporation)
DAT Video CD MPEG or MPEG1 Movie
DAT VCD and/or SVCD File
DAT Mitsubishi DJ-1000 and Photorun Native Format
DAT Clarion DOS Database (SoftVelocity)
DAT PestPatrol Data/Scan Strings (PestPatrol, Inc.)
DAT EasyRecovery Saved Recovery State (Kroll Ontrack Inc.)
DAT Oric Atmos Snapshot
DAT Allegro Generic Data
DAT Windows 9x Registry Hive (Microsoft Corporation)
DAT BLUEWAVE File
DAT Data
DAT MapInfo Native Data Format (Mapinfo Corporation)
DAT Internet Explorer Cache File (Microsoft)
DAT Walkman NW-S23 MP3 File Storage Container (Sony)
DAT Gunlok Archive
DAT Commodore 64 Audio
DAT Exchange Server Error Message (WINMAIL.DAT) (Microsoft Corporation)
DAT Digital Audio Tape
Any OpenSource player can convert them or access them for free.
http://xinehq.de/
What is xine?
xine is a free multimedia player. It plays back CDs, DVDs, and VCDs. It also decodes multimedia files like AVI, MOV, WMV, and MP3 from local disk drives, and displays multimedia streamed over the Internet. It interprets many of the most common multimedia formats available - and some of the most uncommon formats, too.
http://en.wikipedia.org/wiki/Xine
Every Linux geek has used Xine or somesuch thing for long time now.
http://audacity.sourceforge.net/
Audacity is another stable one.
Why do you think Micro/Applesoft bought a Linux Distro.