First off, you do NOT have a "Dell vectra vl400 dt" because one of these was never made in this universe.
You "Might" have a Hp vectra vl400 dt and Hp does not extend support beyond Windows 2000.
You are not totally screwed yet. You can download a program that will identify what you do have and what the sound card really is. Download and run this program (Belarc) and report back with it's findings.