DVD Decoder Issues

Hi

My old CD-R drive died. At the time, I wanted a replacement drive to keep doing what I was doing - namely burn music CD's. I took my CPU to a tech who installed a new combo SONY CRX320E CD-RW/DVD-RAM drive. After the fix, I discovered I now could watch DVD/DVD-ROM's on my computer. Included with the drive was the following DVD software:

Interactual Player 2.0

When I push play on an inserted DVD, I get this message:

''Playback failed due to a problem with the
video subsystem. Lowering your screen resolution or color depth may fix the problem.''

Lowering screen resolution didn't help.

I use diagnostics found in the Interactual 2.0 Help Menu and I get this result:

''Decoder Provider:
Decoder Type:
Decoder Name:
Decoder Version:
Decoder Driver Date:
Navigator Name:
Navigator Version: 0
Is DVD Device Found: No''

So it looks like I need to purchase a DVD Decoder even though I have Interactual 2.0 installed on my HD? Why didn't the decoder come with the software? The tech saysd I need to buy a decoder.

The recommended decoder is WinDVD 7.0. Will this decoder limit my DVD viewing capabilities? Are there any security issues if I get this software online?

Thanks

Dell Dimension 4100 Series PIII at 866MHz
512MB SDRAM at 133MHz
40GB Ultra ATA HD (7200rpm)
Turtle Beach Santa Cruz DSP Sound Card
Dell P780 on 32MB DDR nVidia GeForce2 GTS 4X APG Graphics Card
SONY CRX320E 52/24/16 CD-RW/DVD-ROM
Firefox 1.0.6
Windows98SE