Newer DVD players have the same audio outputs of older DVD players - optical and/or coaxial digital, stereo left/right, and some have built-in DD/DTS decoding and therefore also have 5.1 analog outs.
If your receiver is really old, it will only have Dolby Pro Logic and won't have Dolby Digital or DTS decoding. If that's the case, it's definitely in your best interests to upgrade your receiver. You can get a perfectly decent receiver for $150 - $200.