Sys­tem en­vi­ron­ment:

• nVidia graph­ics card
• Win­dows Vis­ta Home Premi­um 32-bit
• 2 GB RAM
• In­te­grat­ed “HD” au­dio

The so­lu­tion for me:

1. Re­mem­ber to set CoD2 to com­pat­i­bil­i­ty mode with Win­dows XP SP2! You can do this by right-click­ing the short­cut and se­lect­ing “Prop­er­ties”, then open­ing the “Com­pat­i­bil­i­ty” tab at the top.
2. First tried up­dat­ing Di­rec­tX 9. Vis­ta users should note that Di­rec­tX 9 and Di­rec­tX 10, while both com­ing pre-in­stalled on Vis­ta, are sep­a­rate com­po­nents. You should still up­date to the lat­est Di­rec­tX 9 even if you have Di­rec­tX 10. Un­for­tu­nate­ly, while a good first step, this didn’t work for me.
3. Then, added “+set com_in­tro­played 1” to the end of the short­cuts. You can do this by open­ing the short­cut prop­er­ties (see step 0) and adding those char­ac­ters, with­out quotes, to the end of the “Tar­get:” box, so that the full line looks like: “C:\Pro­gram Files\Ac­tivi­sion\Call of Du­ty 2\cod2sp_s.exe” +set com_in­tro­played 1 This fixed the sin­gle-play­er for me, but I still could not open mul­ti­play­er.
4. I found on NT­com­pat­i­ble.com a seem­ing­ly-ridicu­lous lit­tle propo­si­tion. The poster sug­gest­ed that, to run CoD2 mul­ti­play­er, one should plug some­thing in to the mi­cro­phone jack. So, I did, and lo and be­hold, it worked! Rather a strange so­lu­tion, I do say. It like­ly has some­thing to do with the in­ter­ac­tion be­tween my in­te­grat­ed au­dio and the voice chat fea­tures of CoD2, so turn­ing off voice chat might al­low it to run with­out a mi­cro­phone plugged in.

Any­ways, that’s how I got this game to work on Vis­ta; hope it helps some­body else too!