Vampire Walter vs The Captain:
Assuming that the heart is the weak point of The Captain's (which it should be seeing it's the weakness of every monster and character in the series), Vampire Walter can defeat him.
http://www.mangahere.com/manga/hellsing/c085/9.htmlWe see Seras's shadow spikes easily stabbing all the way through The Captain's body.
Assuming that his wires are as deadly and sharp as Seras's shadow arm spikes, the wire should be able to cut into the Captain's body and tear up his heart, thus killing him.
Of course, that's assuming that this is a stabilized vampire Walter and The Captain stays in his human form. If he goes in his werewolf form, good luck to Walter. Because he'll be needing silver for this job.
Nail Alexander Anderson vs Vampire Walter:
Walter. Faster, longer range of attack, faster attacks, and wires can effortlessly slice into Anderson's flesh. Walter doesn't even have to move.
The Captain vs Alexander Anderson:
The Captain in human form may only beat human Anderson with extreme difficulty. Other than that, even if the captain is in his werewolf forms, Nail Anderson will slice him up and roast him.
Alucard vs The Captain:
Alucard. Always.